Make of list of at least three organisms that Make of list of at least three organisms that reproduce asexually and three organisms that reproduce asexually and three organisms that reproduce sexually.reproduce sexually.

► In asexual reproduction, how does the offspring In asexual reproduction, how does the offspring compare to the parent?compare to the parent?

► In sexual reproduction, how does the offspring In sexual reproduction, how does the offspring compare to the parent?compare to the parent?

► Why are chromosomes important to an Why are chromosomes important to an organism?organism?

► In In asexual reproductionasexual reproduction, a single parent passes a , a single parent passes a complete copy of its genetic information to each of complete copy of its genetic information to each of its offspring. its offspring.

► An individual formed by asexual reproduction is An individual formed by asexual reproduction is genetically identical to its parent.genetically identical to its parent.

► Prokaryotes reproduce asexually by a kind of cell Prokaryotes reproduce asexually by a kind of cell division called division called binary fission. binary fission.

► Many unicellular eukaryotes also reproduce Many unicellular eukaryotes also reproduce asexually.asexually.

► Some multicellular eukaryotes, such as starfish, Some multicellular eukaryotes, such as starfish, go through fragmentation. go through fragmentation.

► Fragmentation Fragmentation is a kind of reproduction in is a kind of reproduction in which the body breaks into several pieces. which the body breaks into several pieces. Some or all of these fragments regrow missing Some or all of these fragments regrow missing parts and develop into complete adults.parts and develop into complete adults.

► Other animals, such as the hydra, go through Other animals, such as the hydra, go through budding. budding. In budding, new individuals split off from In budding, new individuals split off from existing ones. existing ones.

► Some plants, such as potatoes, can form whole Some plants, such as potatoes, can form whole new plants from parts of stems. new plants from parts of stems.

► Other plants can reproduce from roots or leaves. Other plants can reproduce from roots or leaves.

► Some crustaceans, such as water fleas, reproduce Some crustaceans, such as water fleas, reproduce by parthenogenesis. by parthenogenesis. Parthenogenesis Parthenogenesis is a process is a process in which a female makes a viable egg that grows in which a female makes a viable egg that grows into an adult without being fertilized by a male.into an adult without being fertilized by a male.

► Most eukaryotic organisms Most eukaryotic organisms reproduce sexually. reproduce sexually.

► In In sexual reproduction,sexual reproduction, two two parents give genetic material to parents give genetic material to produce offspring that are produce offspring that are genetically different from their genetically different from their parents. parents.

► Each parent produces a Each parent produces a reproductive cell, called a reproductive cell, called a gamete.gamete. A gamete from one A gamete from one parent fuses with a gamete from parent fuses with a gamete from the other. the other.

Visual Concept: Visual Concept: Sexual Sexual ReproductionReproduction

► The resulting cell, called a The resulting cell, called a zygote,zygote, has a has a combination of genetic material from both combination of genetic material from both parents. This process is called parents. This process is called fertilizationfertilization. .

► Because both parents give genetic material, the Because both parents give genetic material, the offspring has traits of both parents but is not offspring has traits of both parents but is not exactly like either parent.exactly like either parent.

Visual Concept: Visual Concept: FertilizationFertilization

Germ Cells and Somatic CellsGerm Cells and Somatic Cells► The cells of a multicellular organism are often The cells of a multicellular organism are often

specialized for certain functions. specialized for certain functions.

► Cells that are specialized for sexual reproduction Cells that are specialized for sexual reproduction are called are called germ cells. germ cells. Only germ cells can Only germ cells can produce gametes. produce gametes.

► Other body cells are called Other body cells are called somatic cells. somatic cells. Somatic Somatic cells do not participate in sexual reproduction.cells do not participate in sexual reproduction.

Advantages of Sexual ReproductionAdvantages of Sexual Reproduction► Asexual reproduction is the simplest, most Asexual reproduction is the simplest, most

efficient method of reproduction. efficient method of reproduction.

► Asexual reproduction allows organisms to Asexual reproduction allows organisms to produce many offspring in a short period of time produce many offspring in a short period of time without using energy to make gametes or to find without using energy to make gametes or to find a mate. a mate.

► But the genetic material of these organisms But the genetic material of these organisms varies little between individuals, so they may be varies little between individuals, so they may be at a disadvantage in a changing environment. at a disadvantage in a changing environment.

Advantages of Sexual ReproductionAdvantages of Sexual Reproduction► Sexual reproduction, in contrast, produces Sexual reproduction, in contrast, produces

genetically diverse individuals. genetically diverse individuals.

► A population of diverse organisms is more likely A population of diverse organisms is more likely to have some individuals that survive a major to have some individuals that survive a major environmental change.environmental change.

► Each chromosome has thousands of genes that Each chromosome has thousands of genes that play an important role in determining how an play an important role in determining how an organism develops and functions. organism develops and functions.

► Each species has a characteristic number of Each species has a characteristic number of chromosomes. chromosomes.

► An organism must have exactly the right number An organism must have exactly the right number of chromosomes. If an organism has too many or of chromosomes. If an organism has too many or too few chromosomes, the organism may not too few chromosomes, the organism may not develop and function properly.develop and function properly.

Visual Concepts: Visual Concepts: Chromosome NumberChromosome Number

Click above to play the video.

Haploid and Diploid CellsHaploid and Diploid Cells► A cell, such as a somatic cell, that has two sets A cell, such as a somatic cell, that has two sets

of chromosomes is of chromosomes is diploid. diploid.

► A cell is A cell is haploidhaploid if it has one set of if it has one set of chromosomes. chromosomes.

► Gametes are haploid cells.Gametes are haploid cells.

Haploid and Diploid CellsHaploid and Diploid Cells► The symbol The symbol n n is used to represent the number is used to represent the number

of chromosomes in one set. of chromosomes in one set.

► Human gametes have 23 chromosomes, so Human gametes have 23 chromosomes, so n n = = 23. The diploid number in somatic cells is 23. The diploid number in somatic cells is written as 2written as 2nn. Human somatic cells have 46 . Human somatic cells have 46 chromosomes (2chromosomes (2n n = 46).= 46).

Click above to play the video.

Homologous ChromosomesHomologous Chromosomes► Each diploid cell has pairs of Each diploid cell has pairs of

chromosomes made up of two chromosomes made up of two homologous chromosomes. homologous chromosomes.

► Homologous chromosomesHomologous chromosomes are chromosomes that are are chromosomes that are similar in size, in shape, and in similar in size, in shape, and in kinds of genes.kinds of genes.

► Each chromosome in a Each chromosome in a homologous pair comes from one homologous pair comes from one of the two parents. of the two parents.

► Homologous chromosomes can Homologous chromosomes can carry different forms of genes. carry different forms of genes.

Visual Concept: Visual Concept: Homologous Homologous ChromosomesChromosomes

Click above to play the video.

Autosomes and Sex ChromosomesAutosomes and Sex Chromosomes► Autosomes Autosomes are chromosomes with genes that are chromosomes with genes that

do not determine the sex of an individual. do not determine the sex of an individual.

► Sex chromosomes Sex chromosomes have genes that determine have genes that determine the sex of an individual.the sex of an individual.

Visual Concept: Visual Concept: Sex Sex Chromosomes and Chromosomes and

AutosomesAutosomes

Autosomes and Sex ChromosomesAutosomes and Sex Chromosomes► In humans and many other organisms, In humans and many other organisms,

the two sex chromosomes are referred the two sex chromosomes are referred to as the to as the X X and and Y chromosomesY chromosomes. .

► The genes that cause a zygote to The genes that cause a zygote to develop into a male are located on the develop into a male are located on the Y chromosome.Y chromosome.

► Human males have one X Human males have one X chromosome and one Y chromosome chromosome and one Y chromosome (XY), and human females have two X (XY), and human females have two X chromosomes (XX).chromosomes (XX).

Visual Concept: Visual Concept: The Role of Sex The Role of Sex Chromosomes in Sex Chromosomes in Sex

DeterminationDetermination

► An individual formed by asexual reproduction is An individual formed by asexual reproduction is genetically identical to its parent.genetically identical to its parent.

► In sexual reproduction, two parents give In sexual reproduction, two parents give genetic material to produce offspring that are genetic material to produce offspring that are genetically different from their parents.genetically different from their parents.

► Each chromosome has thousands of genes that Each chromosome has thousands of genes that play an important role in determining how an play an important role in determining how an organism develops and functions.organism develops and functions.

If a human sperm and egg each had 46 If a human sperm and egg each had 46 chromosomes, how many chromosomes would a chromosomes, how many chromosomes would a fertilized egg have? Explain why increasing the fertilized egg have? Explain why increasing the number of chromosomes a human cell might number of chromosomes a human cell might cause problems.cause problems.

► What occurs during the stages of meiosis?What occurs during the stages of meiosis?

► How does the function of mitosis differ from the How does the function of mitosis differ from the function of meiosis?function of meiosis?

► What are three mechanisms of genetic What are three mechanisms of genetic variation?variation?

► MeiosisMeiosis is a form of cell division that produces is a form of cell division that produces daughter cells with half the number of daughter cells with half the number of chromosomes that are in the parent cell.chromosomes that are in the parent cell.

► During meiosis, a diploid cell goes through two During meiosis, a diploid cell goes through two divisions to form four haploid cells. divisions to form four haploid cells.

► In meiosis I, homologous chromosomes are In meiosis I, homologous chromosomes are separated. In meiosis II, the sister chromatids of separated. In meiosis II, the sister chromatids of each homologue are separated. each homologue are separated.

Visual Concept: Visual Concept: MeiosisMeiosis

Click above to play the video.

Meiosis IMeiosis I► Meiosis begins with a diploid cell that has copied its Meiosis begins with a diploid cell that has copied its

chromosomes. chromosomes.

► During prophase I, the chromosomes condense, and During prophase I, the chromosomes condense, and the nuclear envelope breaks down. Homologous the nuclear envelope breaks down. Homologous chromosomes pair. Chromatids exchange genetic chromosomes pair. Chromatids exchange genetic material in a process called material in a process called crossing-overcrossing-over. .

► In metaphase I, the spindle moves the pairs of In metaphase I, the spindle moves the pairs of homologous chromosomes to the equator of the cell. homologous chromosomes to the equator of the cell. The homologous chromosomes remain together. The homologous chromosomes remain together.

Meiosis IMeiosis I► In anaphase I, the homologous chromosomes In anaphase I, the homologous chromosomes

separate. The spindle fibers pull the chromosomes separate. The spindle fibers pull the chromosomes of each pair to opposite poles of the cell. But the of each pair to opposite poles of the cell. But the chromatids do not separate at their centromeres. chromatids do not separate at their centromeres. Each chromosome is still made of two chromatids. Each chromosome is still made of two chromatids. The genetic material, however, has recombined. The genetic material, however, has recombined.

► During telophase I, the cytoplasm divides During telophase I, the cytoplasm divides (cytokinesis), and two new cells are formed. Both (cytokinesis), and two new cells are formed. Both cells have one chromosome from each pair of cells have one chromosome from each pair of homologous chromosomes.homologous chromosomes.

Meiosis IIMeiosis II► Meiosis II begins with the two cells formed at Meiosis II begins with the two cells formed at

the end of telophase I of meiosis I. the end of telophase I of meiosis I.

► The chromosomes are not copied between The chromosomes are not copied between meiosis I and meiosis II. meiosis I and meiosis II.

► In prophase II, new spindles form.In prophase II, new spindles form.

► During metaphase II, the chromosomes line During metaphase II, the chromosomes line up along the equators and are attached at up along the equators and are attached at their centromeres to spindle fibers.their centromeres to spindle fibers.

Meiosis IIMeiosis II► In anaphase II, the centromeres divide. The In anaphase II, the centromeres divide. The

chromatids, which are now called chromatids, which are now called chromosomes, chromosomes, move to opposite poles of the cell.move to opposite poles of the cell.

► During telophase II, a nuclear envelope forms During telophase II, a nuclear envelope forms around each set of chromosomes. The spindle around each set of chromosomes. The spindle breaks down, and the cell goes through breaks down, and the cell goes through cytokinesis. cytokinesis.

► The result of meiosis is four haploid cells.The result of meiosis is four haploid cells.

► The processes of mitosis and meiosis are similar The processes of mitosis and meiosis are similar but meet different needs and have different but meet different needs and have different results. results.

► Mitosis makes new cells that are used during Mitosis makes new cells that are used during growth, development, repair, and asexual growth, development, repair, and asexual reproduction. reproduction.

► Meiosis makes cells that enable an organism to Meiosis makes cells that enable an organism to reproduce sexually and happens only in reproduce sexually and happens only in reproductive structures. reproductive structures.

► Mitosis produces two genetically identical Mitosis produces two genetically identical diploid cells. diploid cells.

► Meiosis produces four genetically different Meiosis produces four genetically different haploid cells. The haploid cells produced by haploid cells. The haploid cells produced by meiosis contain half the genetic information of meiosis contain half the genetic information of the parent cell.the parent cell.

► If you compare meiosis and mitosis, they may If you compare meiosis and mitosis, they may appear similar but they are very different. appear similar but they are very different.

► In prophase I of meiosis, every chromosome pairs In prophase I of meiosis, every chromosome pairs with its homologue. A pair of homologous with its homologue. A pair of homologous chromosomes is called a chromosomes is called a tetrad.tetrad.

► As the tetrads form, different homologues As the tetrads form, different homologues exchange parts of their chromatids in the process exchange parts of their chromatids in the process of crossing-over. The pairing of homologous of crossing-over. The pairing of homologous chromosomes and the crossing-over do not chromosomes and the crossing-over do not happen in mitosis.happen in mitosis.

► Therefore, a main difference between meiosis Therefore, a main difference between meiosis and mitosis is that in meiosis, genetic information and mitosis is that in meiosis, genetic information is rearranged leading to genetic variation in is rearranged leading to genetic variation in offspring.offspring.

Visual Concept: Visual Concept: Comparing Comparing Meiosis and MitosisMeiosis and Mitosis

Visual Concept: Visual Concept: Comparing Comparing the Results of Meiosis and the Results of Meiosis and

MitosisMitosis

► Genetic variation is advantageous for a Genetic variation is advantageous for a population. population.

► Genetic variation can help a population survive Genetic variation can help a population survive a major environmental change. a major environmental change.

► Genetic variation is made possible by sexual Genetic variation is made possible by sexual reproduction. reproduction.

► In sexual reproduction, existing genes are In sexual reproduction, existing genes are rearranged. Meiosis is the process that makes rearranged. Meiosis is the process that makes the rearranging of genes possible. the rearranging of genes possible.

► Fusion of haploid cells from two different Fusion of haploid cells from two different individuals adds further variation.individuals adds further variation.

► Three key contributions to genetic variation are Three key contributions to genetic variation are crossing-over, independent assortment, and crossing-over, independent assortment, and random fertilization.random fertilization.

Crossing-OverCrossing-Over► During prophase I, homologous chromosomes During prophase I, homologous chromosomes

line up next to each other. line up next to each other.

► Each homologous chromosome is made of two Each homologous chromosome is made of two sister chromatids attached at the centromere. sister chromatids attached at the centromere.

► Crossing-over happens when one arm of a Crossing-over happens when one arm of a chromatid crosses over the arm of the other chromatid crosses over the arm of the other chromatid. chromatid.

Crossing-OverCrossing-Over► The chromosomes break at The chromosomes break at

the point of the crossover, the point of the crossover, and each chromatid re-forms and each chromatid re-forms its full length with the piece its full length with the piece from the other chromosome. from the other chromosome.

► Thus, the sister chromatids Thus, the sister chromatids of a homologous of a homologous chromosome no longer have chromosome no longer have identical genetic information.identical genetic information.

Visual Concept: Visual Concept: Tetrads and Tetrads and Crossing-Over of Genetic Crossing-Over of Genetic

MaterialMaterial

Independent AssortmentIndependent Assortment► During metaphase I, homologous pairs of During metaphase I, homologous pairs of

chromosomes line up at the equator of the cell. chromosomes line up at the equator of the cell.

► The two pairs of chromosomes can line up in The two pairs of chromosomes can line up in either of two equally probable ways. either of two equally probable ways.

► This random distribution of homologous This random distribution of homologous chromosomes during meiosis is called chromosomes during meiosis is called independent assortment.independent assortment.

Visual Concept: Visual Concept: Independent Independent AssortmentAssortment

Random FertilizationRandom Fertilization► Fertilization is a random process that adds Fertilization is a random process that adds

genetic variation. genetic variation.

► The zygote that forms is made by the random The zygote that forms is made by the random joining of two gametes. joining of two gametes.

► Because fertilization of an egg by a sperm is Because fertilization of an egg by a sperm is random, the number of possible outcomes is random, the number of possible outcomes is squared. squared.

► During meiosis, a diploid cell goes through two During meiosis, a diploid cell goes through two divisions to form four haploid cells.divisions to form four haploid cells.

► Mitosis produces cells that are used during Mitosis produces cells that are used during growth, development, repair, and asexual growth, development, repair, and asexual reproduction. Meiosis makes cells that enable an reproduction. Meiosis makes cells that enable an organism to reproduce sexually and it only organism to reproduce sexually and it only happens in reproductive structures.happens in reproductive structures.

► Three key contributions to genetic variation are Three key contributions to genetic variation are crossing-over, independent assortment, and crossing-over, independent assortment, and random fertilization.random fertilization.

Write a sentence using each one of the following Write a sentence using each one of the following terms: haploid, diploid, zygote.terms: haploid, diploid, zygote.

► What is a diploid life cycle?What is a diploid life cycle?

► What is a haploid life cycle?What is a haploid life cycle?

► What is alternation of generations?What is alternation of generations?

► Most animals have a diploid life cycle. Most animals have a diploid life cycle.

► Most of the life cycle is spent in the diploid Most of the life cycle is spent in the diploid state. state.

► All of the cells except the gametes are diploid.All of the cells except the gametes are diploid.

► A diploid germ cell in a reproductive organ goes A diploid germ cell in a reproductive organ goes through meiosis and forms gametes. through meiosis and forms gametes.

► The gametes, the sperm and the egg, join during The gametes, the sperm and the egg, join during fertilization. The result is a diploid zygote. fertilization. The result is a diploid zygote.

► This single diploid cell goes through mitosis and This single diploid cell goes through mitosis and eventually gives rise to all of the cells of the eventually gives rise to all of the cells of the adult, which are also diploid. adult, which are also diploid.

► In diploid life cycles, meiosis in germ cells of a In diploid life cycles, meiosis in germ cells of a multicellular diploid organism results in the multicellular diploid organism results in the formation of haploid gametes.formation of haploid gametes.

Meiosis and Gamete FormationMeiosis and Gamete Formation► Male animals produce gametes called Male animals produce gametes called sperm.sperm.

► A diploid germ cell goes through meiosis I. Two cells A diploid germ cell goes through meiosis I. Two cells are formed, each of which goes through meiosis II. are formed, each of which goes through meiosis II.

► The result is four haploid cells. The result is four haploid cells.

► The four cells change in form and develop a tail to The four cells change in form and develop a tail to form four sperm.form four sperm.

Visual Concept: Visual Concept: Formation of Formation of SpermSperm

Click above to play the video.

Meiosis and Gamete FormationMeiosis and Gamete Formation► Female animals produce gametes called eggs, Female animals produce gametes called eggs,

or ova (singular, or ova (singular, ovumovum). ).

► A diploid germ cell begins to divide by meiosis. A diploid germ cell begins to divide by meiosis. Meiosis I results in the formation of two haploid Meiosis I results in the formation of two haploid cells that have unequal amounts of cytoplasm. cells that have unequal amounts of cytoplasm.

► One of the cells has nearly all of the cytoplasm. One of the cells has nearly all of the cytoplasm. The other cell, called a The other cell, called a polar body, polar body, is very small is very small and has a small amount of cytoplasm. and has a small amount of cytoplasm.

Meiosis and Gamete FormationMeiosis and Gamete Formation► The polar body may divide again, but its The polar body may divide again, but its

offspring cells will not survive. offspring cells will not survive.

► The larger cell goes through meiosis II, and the The larger cell goes through meiosis II, and the division of the cell’s cytoplasm is again division of the cell’s cytoplasm is again unequal. unequal.

► The larger cell develops into an ovum. The The larger cell develops into an ovum. The smaller cell, the second polar body, dies. smaller cell, the second polar body, dies.

Meiosis and Gamete FormationMeiosis and Gamete Formation► Because of its larger share of cytoplasm, the Because of its larger share of cytoplasm, the

mature ovum has a rich storehouse of mature ovum has a rich storehouse of nutrients. nutrients.

► These nutrients nourish the young organism These nutrients nourish the young organism that develops if the ovum is fertilized.that develops if the ovum is fertilized.

Visual Concept: Visual Concept: Formation of Formation of the Egg Cellthe Egg Cell

Click above to play the video.

► The haploid life cycle happens in most fungi The haploid life cycle happens in most fungi and some protists. and some protists.

► Haploid stages make up the major part of this Haploid stages make up the major part of this life cycle. life cycle.

► The zygote, the only diploid structure, goes The zygote, the only diploid structure, goes through meiosis immediately after it is formed through meiosis immediately after it is formed and makes new haploid cells. and makes new haploid cells.

► The haploid cells divide by mitosis and give rise The haploid cells divide by mitosis and give rise to multicellular haploid individuals. to multicellular haploid individuals.

► In haploid life cycles, meiosis in a diploid zygote In haploid life cycles, meiosis in a diploid zygote results in the formation of the first cell of a results in the formation of the first cell of a multicellular haploid individual.multicellular haploid individual.

► Plants and most multicellular protists have a life Plants and most multicellular protists have a life cycle that alternates between a haploid phase cycle that alternates between a haploid phase and a diploid phase called and a diploid phase called alternation of alternation of generations. generations.

► In plants, the multicellular diploid phase in the In plants, the multicellular diploid phase in the life cycle is called a life cycle is called a sporophyte. sporophyte.

► Spore-forming cells in the sporophyte undergo Spore-forming cells in the sporophyte undergo meiosis and produce spores. meiosis and produce spores.

► A spore forms a multicellular gametophyte.A spore forms a multicellular gametophyte.

► The The gametophyte gametophyte is the haploid phase that is the haploid phase that produces gametes by mitosis. produces gametes by mitosis.

► The gametes fuse and give rise to the diploid The gametes fuse and give rise to the diploid phase.phase.

Visual Concept: Visual Concept: Alternation Alternation of Generationsof Generations

► In diploid life cycles, meiosis in germ cells of a In diploid life cycles, meiosis in germ cells of a multicellular diploid organism results in the multicellular diploid organism results in the formation of haploid gametes.formation of haploid gametes.

► In haploid life cycles, meiosis in a diploid zygote In haploid life cycles, meiosis in a diploid zygote results in the formation of the first cell of a results in the formation of the first cell of a multicellular haploid individual.multicellular haploid individual.

► Plants and most multicellular protists have a life Plants and most multicellular protists have a life cycle that alternates between a haploid phase cycle that alternates between a haploid phase and a diploid phase called and a diploid phase called alternation of alternation of generationsgenerations..

List five characteristics that are passed on in List five characteristics that are passed on in families. families.

Name one characteristic that is inherited but that Name one characteristic that is inherited but that may also be influenced by behavior or may also be influenced by behavior or environment.environment.

► Why was Gregor Mendel important for modern Why was Gregor Mendel important for modern genetics?genetics?

► Why did Mendel conduct experiments with Why did Mendel conduct experiments with garden peas?garden peas?

► What were the important steps in Mendel’s first What were the important steps in Mendel’s first experiments?experiments?

► What were the important results of Mendel’s first What were the important results of Mendel’s first experiments?experiments?

► the study of heredity the study of heredity

► A monk named Gregor Mendel did A monk named Gregor Mendel did breeding experiments in the 1800s breeding experiments in the 1800s with the garden pea plant.with the garden pea plant.

► The science of heredity and the The science of heredity and the mechanism by which traits are passed mechanism by which traits are passed from parents to offspring is called from parents to offspring is called genetics.genetics.

► Modern genetics is based on Mendel’s Modern genetics is based on Mendel’s explanations for the patterns of explanations for the patterns of heredity in garden pea plants.heredity in garden pea plants.

► Most of Mendel’s experiments involved Most of Mendel’s experiments involved crossing different types of pea plants. crossing different types of pea plants. In this case, the word In this case, the word crosscross means “to means “to mate or breed two individuals.”mate or breed two individuals.”

► The garden pea plant is a good subject The garden pea plant is a good subject for studying heredity because the plant for studying heredity because the plant has contrasting traits, usually self-has contrasting traits, usually self-pollinates, and grows easily.pollinates, and grows easily.

► In the study of heredity, physical In the study of heredity, physical features that are inherited are called features that are inherited are called characters.characters.

► A A trait trait is one of several possible forms is one of several possible forms of a character.of a character.

► The offspring of a cross between The offspring of a cross between parents that have contrasting traits is parents that have contrasting traits is called a called a hybrid.hybrid.

► In garden pea plants, each flower In garden pea plants, each flower contains both male and female contains both male and female reproductive parts. This reproductive parts. This arrangement allows the plant to arrangement allows the plant to self-pollinate,self-pollinate, or fertilize itself. or fertilize itself.

► Cross-pollinationCross-pollination occurs when occurs when pollen from the flower of one pollen from the flower of one plant is carried by insects or by plant is carried by insects or by other means to the flower of other means to the flower of another plant. another plant.

► Mendel cross-pollinated pea Mendel cross-pollinated pea plants by removing the male plants by removing the male parts from some of the flowers parts from some of the flowers then dusting the female parts then dusting the female parts with pollen from another plant.with pollen from another plant.

Mendel controlled thefertilization of his pea plantsby removing the male parts,or stamens.

He then fertilized the femalepart, or pistil, with pollen froma different pea plant.

► The garden pea is a good subject for studying The garden pea is a good subject for studying heredity because it matures quickly and heredity because it matures quickly and produces many offspring.produces many offspring.

► Thus, Mendel was able to compare several Thus, Mendel was able to compare several results for each type of cross and collect results for each type of cross and collect repeated data.repeated data.

► Collecting repeated data is an important Collecting repeated data is an important scientific method.scientific method.

► A A monohybrid crossmonohybrid cross is a cross that is done to is a cross that is done to study one pair of contrasting traits. Crossing a study one pair of contrasting traits. Crossing a plant that has purple flowers with a plant that plant that has purple flowers with a plant that has white flowers is an example of a has white flowers is an example of a monohybrid cross. monohybrid cross.

► Mendel’s first experiments used monohybrid Mendel’s first experiments used monohybrid crosses and were carried out in three steps.crosses and were carried out in three steps.

► Each step involved a new generation of plants. Each step involved a new generation of plants. A A generationgeneration is a group of offspring from a is a group of offspring from a given group of parents.given group of parents.

► Plants that self-pollinate for several generations Plants that self-pollinate for several generations produce offspring of the same type. Such a plant produce offspring of the same type. Such a plant is said to be is said to be true-breedingtrue-breeding for a given trait. for a given trait.

► The first group of parents that are crossed in a The first group of parents that are crossed in a breeding experiment are called the breeding experiment are called the parental parental generationgeneration or or P generation. P generation. The offspring of the P The offspring of the P generation is called the generation is called the first filial generation,first filial generation, or or FF11 generation. generation.

► Mendel allowed the FMendel allowed the F11 generation to self-pollinate generation to self-pollinate and produce new plants. He called this offspring and produce new plants. He called this offspring the the second filial generation,second filial generation, or or FF22 generation. generation.

Visual Concept: Visual Concept: Mendel’s Mendel’s ExperimentsExperiments

► All of Mendel’s FAll of Mendel’s F11 plants expressed the same trait for a given plants expressed the same trait for a given character. The contrasting trait seemed to have disappeared.character. The contrasting trait seemed to have disappeared.

► The contrasting trait reappeared, however, in some of the FThe contrasting trait reappeared, however, in some of the F22 plants when the Fplants when the F11 plants were allowed to self-pollinate. plants were allowed to self-pollinate.

► For each of the seven characters that Mendel studied, he For each of the seven characters that Mendel studied, he found a similar 3-to-1 ratio of contrasting traits in the Ffound a similar 3-to-1 ratio of contrasting traits in the F22 generation.generation.

► Modern genetics is based on Mendel’s explanations for the Modern genetics is based on Mendel’s explanations for the patterns of heredity that he studied in garden pea plants.patterns of heredity that he studied in garden pea plants.

► The garden pea plant is a good subject for studying The garden pea plant is a good subject for studying heredity because the plant has contrasting traits, usually heredity because the plant has contrasting traits, usually self-pollinates, and grows easily.self-pollinates, and grows easily.

► Mendel’s first experiments used monohybrid crosses and Mendel’s first experiments used monohybrid crosses and were carried out in three steps.were carried out in three steps.

► For each of the seven characters that Mendel studied, he For each of the seven characters that Mendel studied, he found a similar 3-to-1 ratio of contrasting traits in the Ffound a similar 3-to-1 ratio of contrasting traits in the F22 generation.generation.

A gardener noticed that some of the flowers on A gardener noticed that some of the flowers on her plants were white. In previous years, they had her plants were white. In previous years, they had been purple.been purple.

Write down a possible explanation for this Write down a possible explanation for this difference.difference.

► What patterns of heredity were explained by What patterns of heredity were explained by Mendel’s hypotheses?Mendel’s hypotheses?

► What is the law of segregation?What is the law of segregation?

► How does genotype relate to phenotype?How does genotype relate to phenotype?

► What is the law of independent assortment?What is the law of independent assortment?

► Mendel developed several hypotheses to explain Mendel developed several hypotheses to explain the results of his experiments.the results of his experiments.

► These hypotheses are collectively called the These hypotheses are collectively called the Mendelian theory of heredityMendelian theory of heredity and form the and form the foundation of modern genetics.foundation of modern genetics.

► Mendelian theory explains simple patterns of Mendelian theory explains simple patterns of inheritance. In these patterns, two of several inheritance. In these patterns, two of several versions of a gene combine and result in one of versions of a gene combine and result in one of several possible traits.several possible traits.

► Different traits result from different versions of Different traits result from different versions of genes. Each version of a gene is called an genes. Each version of a gene is called an allele.allele.

Visual Concept: Visual Concept: AlleleAllele

Click above to play the video.

► Each allele can lead to a unique trait.Each allele can lead to a unique trait.

► Traits can come from either parent because Traits can come from either parent because each pair of alleles is separated when each pair of alleles is separated when gametes form during meiosis.gametes form during meiosis.

► Only one of the pair is passed on to offspring.Only one of the pair is passed on to offspring.

► An allele that is fully expressed whenever it is An allele that is fully expressed whenever it is present is called present is called dominant.dominant.

► An allele that is not expressed when a An allele that is not expressed when a dominant allele is present is called dominant allele is present is called recessive. recessive.

► A recessive allele is expressed only when A recessive allele is expressed only when there is no dominant allele present.there is no dominant allele present.

► Traits may also be called dominant or Traits may also be called dominant or recessive.recessive.

Visual Concept: Visual Concept: Comparing Comparing Dominant and Recessive Dominant and Recessive

TraitsTraits

Click above to play the video.

► Because chromosome pairs split randomly Because chromosome pairs split randomly during meiosis, either one of a pair of during meiosis, either one of a pair of homologous chromosomes might end up in any homologous chromosomes might end up in any one gamete. Chance decides which alleles will one gamete. Chance decides which alleles will be passed on.be passed on.

► In modern terms, the In modern terms, the law of segregationlaw of segregation holds holds that when an organism produces gametes, that when an organism produces gametes, each pair of alleles is separated and each each pair of alleles is separated and each gamete has an equal chance of receiving either gamete has an equal chance of receiving either one of the alleles.one of the alleles.

► Scientists use a code of letters to represent the Scientists use a code of letters to represent the function of alleles.function of alleles.

► A dominant allele is shown as a capital letter. This A dominant allele is shown as a capital letter. This letter usually corresponds to the first letter of the letter usually corresponds to the first letter of the word for the trait. word for the trait.

► A recessive allele is shown as a lowercase letter.A recessive allele is shown as a lowercase letter.

► Offspring do not show a trait for every allele that Offspring do not show a trait for every allele that they receive. Instead, combinations of alleles they receive. Instead, combinations of alleles determine traits.determine traits.

► The set of specific The set of specific combinations of alleles that an combinations of alleles that an individual has for a character is individual has for a character is called the called the genotype.genotype.

► The detectable trait that The detectable trait that results from the genotype’s set results from the genotype’s set of alleles is called the of alleles is called the phenotype.phenotype.

► Thus, genotype determines Thus, genotype determines phenotype.phenotype.

Visual Concept: Visual Concept: GenotypeGenotype

Click above to play the video.

Visual Concept: Visual Concept: Comparing Comparing Genotype and PhenotypeGenotype and Phenotype

► If an individual has two If an individual has two identical alleles of a identical alleles of a certain gene, the individual certain gene, the individual is is homozygoushomozygous for the for the related character.related character.

► If an individual has two If an individual has two different alleles of a different alleles of a certain gene, the individual certain gene, the individual is is heterozygousheterozygous for the for the related character.related character.

Visual Concept: Visual Concept: Comparing Comparing Homozygous and Heterozygous Homozygous and Heterozygous

Genotypes and Resulting Genotypes and Resulting PhenotypesPhenotypes

► A A dihybrid crossdihybrid cross involves two characters, such as involves two characters, such as seed color and seed shape.seed color and seed shape.

► Mendel used dihybrid crosses in his second Mendel used dihybrid crosses in his second experiments and found that the inheritance of experiments and found that the inheritance of one character did not affect the inheritance of one character did not affect the inheritance of another character.another character.

► In modern terms, the In modern terms, the law of independent law of independent assortmentassortment holds that during gamete formation, holds that during gamete formation, the alleles of each gene segregate independently.the alleles of each gene segregate independently.

Independent Assortment in Peas

► Genes are said to be Genes are said to be linkedlinked when they are close when they are close together on chromosomes. together on chromosomes.

► Scientists now know that many genes are linked to Scientists now know that many genes are linked to each other as parts of chromosomes.each other as parts of chromosomes.

► Genes that are located close together on the same Genes that are located close together on the same chromosome will rarely separate independently.chromosome will rarely separate independently.

► The only genes that follow Mendel’s law of The only genes that follow Mendel’s law of independent assortment are those that are far independent assortment are those that are far apart.apart.

► Mendelian theory explains simple patterns of Mendelian theory explains simple patterns of inheritance. In these patterns, two of several inheritance. In these patterns, two of several versions of a gene combine and result in one of versions of a gene combine and result in one of several possible traits.several possible traits.

► In modern terms, the In modern terms, the law of segregationlaw of segregation holds that holds that when an organism produces gametes, each pair of when an organism produces gametes, each pair of alleles is separated and each gamete has an alleles is separated and each gamete has an equal chance of receiving either one of the alleles.equal chance of receiving either one of the alleles.

► Genotype determines phenotype.Genotype determines phenotype.

► In modern terms, the In modern terms, the law of independent law of independent assortmentassortment holds that during gamete holds that during gamete formation, the alleles of each gene segregate formation, the alleles of each gene segregate independently.independently.

Since the dawn of agriculture, people have used Since the dawn of agriculture, people have used selective breeding to improve crops and selective breeding to improve crops and domestic animals. Modern applications of domestic animals. Modern applications of Mendelian genetics and gene technology have Mendelian genetics and gene technology have resulted in major changes in crops and animals. resulted in major changes in crops and animals.

List some examples of selective breeding in List some examples of selective breeding in domestic animals or crops that you know of. domestic animals or crops that you know of.

Explain how you might go about selecting for a Explain how you might go about selecting for a particular trait.particular trait.

► How can a Punnett square be used in genetics? How can a Punnett square be used in genetics?

► How can mathematical probability be used in How can mathematical probability be used in genetics?genetics?

► What information does a pedigree show?What information does a pedigree show?

► A A Punnett squarePunnett square is a model that predicts the is a model that predicts the likely outcomes of a genetic cross.likely outcomes of a genetic cross.

► A Punnett square shows all of the genotypes A Punnett square shows all of the genotypes that could result from a given cross.that could result from a given cross.

► The simplest Punnett square consists of a The simplest Punnett square consists of a square divided into four boxes.square divided into four boxes.

► The combination of letters in each box The combination of letters in each box represents one possible genotype in the represents one possible genotype in the offspring.offspring.

Visual Concept: Visual Concept: Punnett Punnett Square with Heterozygous Square with Heterozygous

CrossCross

► In a monohybrid homozygous cross, all of the In a monohybrid homozygous cross, all of the offspring will be heterozygous (offspring will be heterozygous (YyYy) and will ) and will express the dominant trait. express the dominant trait.

► In a monohybrid heterozygous cross the In a monohybrid heterozygous cross the genotypic ratio will be 1 genotypic ratio will be 1 YYYY : 2 : 2 YyYy : 1 : 1 yyyy. The . The phenotypic ratio will be 3 : 1.phenotypic ratio will be 3 : 1.

► A Punnett square shows the possible outcomes A Punnett square shows the possible outcomes of a cross, but it can also be used to calculate of a cross, but it can also be used to calculate the probability of each outcome.the probability of each outcome.

► ProbabilityProbability is the likelihood that a specific is the likelihood that a specific event will occur.event will occur.

► Probability can be calculated and expressed in Probability can be calculated and expressed in many ways.many ways.

► Probability can be expressed in words, as a Probability can be expressed in words, as a decimal, as a percentage, or as a fraction.decimal, as a percentage, or as a fraction.

devised by R. C. devised by R. C. Punnett Punnett

used to predict results used to predict results of a cross of a cross

assign the traits letters assign the traits letters dominant alleles are dominant alleles are

capitalized capitalized recessive alleles are recessive alleles are

lower case lower case

►W= purple W= purple ►w = white w = white

Tt X Tt Cross

Tt X Tt Cross

► Homozygous Homozygous ParentsParents

► WW x ww WW x ww

► all are Ww - genotype all are Ww - genotype which is heterozygous which is heterozygous

► purple - phenotype purple - phenotype

► Heterozygous Heterozygous ParentsParents

► Ww x Ww Ww x Ww

► 25% WW = purple 25% WW = purple ► 50% Ww = purple 50% Ww = purple ► 25% ww = white25% ww = white

Is there a way to determine Is there a way to determine genotypes of organisms?genotypes of organisms? If recessive, it is homozygous. If recessive, it is homozygous.

► TestcrossTestcross unknown genotype crossed unknown genotype crossed

with known genotype with known genotype (recessive trait) (recessive trait)

► white with purple white with purple ► genotype HAS to be either genotype HAS to be either

WW or WwWW or Ww► resulting generation will resulting generation will

answer the questionanswer the question

Visual Concept: Visual Concept: Calculating Calculating ProbabilityProbability

► Probability formulas can be used to predict the Probability formulas can be used to predict the probabilities that specific alleles will be passed probabilities that specific alleles will be passed on to offspring.on to offspring.

► The possible results of a heterozygous cross The possible results of a heterozygous cross are similar to those of flipping two coins at are similar to those of flipping two coins at once.once.

► A A pedigreepedigree is a diagram that shows how a trait is a diagram that shows how a trait is inherited over several generations of a family.is inherited over several generations of a family.

► Pedigrees can be used to help a family Pedigrees can be used to help a family understand a genetic disorder.understand a genetic disorder.

► A A genetic disordergenetic disorder is a disease or disorder that is a disease or disorder that can be inherited.can be inherited.

► A pedigree can help answer questions about A pedigree can help answer questions about three aspects of inheritance: sex linkage, three aspects of inheritance: sex linkage, dominance, and heterozygosity.dominance, and heterozygosity.

A circle represents a female.

A square represents a male.

A horizontal line connecting a male and female represents a marriage.

A vertical line and a bracket connect the parents to their children.A half-shaded

circle or square indicates that a person is a carrier of the trait.

A completely shaded circle or square indicates that a person expresses the trait.

A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait.

A Pedigree

A diagram that shows how a trait is inherited in a family

Visual Concept: Visual Concept: PedigreePedigree

► The sex chromosomes, X and Y, carry genes for The sex chromosomes, X and Y, carry genes for many characters other than gender.many characters other than gender.

► A A sex-linked genesex-linked gene is located on either an X or a is located on either an X or a Y chromosome.Y chromosome.

► Traits that are not expressed equally in both Traits that are not expressed equally in both sexes are commonly sex-linked traits.sexes are commonly sex-linked traits.

► Colorblindness is an example of a sex-linked Colorblindness is an example of a sex-linked trait that is expressed more in males than in trait that is expressed more in males than in females. females.

Visual Concept: Visual Concept: Sex LinkageSex Linkage

► If a person has a trait that is autosomal and If a person has a trait that is autosomal and dominant and has even one dominant allele, he dominant and has even one dominant allele, he or she will show the trait.or she will show the trait.

► If a person has a recessive trait and only one If a person has a recessive trait and only one recessive allele, he or she will not show the trait recessive allele, he or she will not show the trait but may pass it on.but may pass it on.

► If a person is either heterozygous or If a person is either heterozygous or homozygous dominant for an autosomal gene, homozygous dominant for an autosomal gene, his or her phenotype will show the dominant his or her phenotype will show the dominant trait.trait.

► If a person is homozygous recessive, his or her If a person is homozygous recessive, his or her phenotype will show the recessive trait.phenotype will show the recessive trait.

► A recessive trait in a child shows that both A recessive trait in a child shows that both parents were heterozygous carriers of that parents were heterozygous carriers of that recessive allele.recessive allele.

► A Punnett square shows all of the genotypes A Punnett square shows all of the genotypes that could result from a given cross.that could result from a given cross.

► Probability formulas can be used to predict the Probability formulas can be used to predict the probabilities that specific alleles will be passed probabilities that specific alleles will be passed on to offspring.on to offspring.

► A pedigree can help answer questions about A pedigree can help answer questions about three aspects of inheritance: sex linkage, three aspects of inheritance: sex linkage, dominance, and heterozygosity.dominance, and heterozygosity.

Study the animals shown in Figure 11. Study the animals shown in Figure 11.

List possible mechanisms that allow the arctic List possible mechanisms that allow the arctic fox to change its fur color with changing fox to change its fur color with changing seasons.seasons.

► Are there exceptions to the simple Mendelian Are there exceptions to the simple Mendelian pattern of inheritance? pattern of inheritance?

► How do heredity and the environment interact How do heredity and the environment interact to influence phenotype?to influence phenotype?

► How do linked genes affect chromosome How do linked genes affect chromosome assortment and crossover during meiosis?assortment and crossover during meiosis?

A)  Complete A)  Complete DominanceDominance

► like we have seen, like we have seen, where one trait is where one trait is completely completely dominant      dominant     

Incomplete Dominance in Four O’Clock Flowers

Incomplete Dominance in Four O’Clock Flowers

C) CodominanceC) Codominance ► when both genes of a when both genes of a

heterozygote are both heterozygote are both fully expressed fully expressed

► neither allele is neither allele is dominant over the dominant over the other other

► horse coat color horse coat color red and white -----> roan red and white -----> roan

Phenotype(Blood TypeGenotype

Antigen on Red Blood Cell

Safe Transfusions

To From

Blood Groups

E) PolygenismE) Polygenism ► controlled by more controlled by more

than 1 pair of genes than 1 pair of genes and have a wide range and have a wide range of phenotypesof phenotypes

► either on same either on same

chromosome or chromosome or different chromosomes different chromosomes

                  ► height, weight, hair, height, weight, hair,

skin color skin color

Visual Concept: Visual Concept: Comparing Comparing Complete, Incomplete, and Complete, Incomplete, and

CodominanceCodominance

► Phenotype can be affected by conditions in the Phenotype can be affected by conditions in the environment, such as nutrients and environment, such as nutrients and temperature.temperature.

► In humans, many characters that are partly In humans, many characters that are partly determined by heredity, such as height, are determined by heredity, such as height, are also affected by the environment.also affected by the environment.

► Many aspects of human personality and Many aspects of human personality and behavior are strongly affected by the behavior are strongly affected by the environment, but genes also play an important environment, but genes also play an important role.role.

► Many traits do not follow Mendel’s laws because Many traits do not follow Mendel’s laws because he studied the simplest kinds of heredity where he studied the simplest kinds of heredity where characters are determined by independent genes.characters are determined by independent genes.

► During meiosis, genes that are close together on During meiosis, genes that are close together on the same chromosome are less likely to be the same chromosome are less likely to be separated than genes that are far apart.separated than genes that are far apart.

► Genes that are close together, as well as the traits Genes that are close together, as well as the traits they determine, are said to be they determine, are said to be linked.linked.

► Linked genes tend to be inherited together.Linked genes tend to be inherited together.

► The Mendelian inheritance pattern is rare in The Mendelian inheritance pattern is rare in nature; other patterns include polygenic nature; other patterns include polygenic inheritance, incomplete dominance, multiple inheritance, incomplete dominance, multiple alleles, and codominance.alleles, and codominance.

► Phenotype can be affected by conditions in the Phenotype can be affected by conditions in the environment, such as nutrients and temperature.environment, such as nutrients and temperature.

► During meiosis, genes that are close together on During meiosis, genes that are close together on the same chromosome are less likely to be the same chromosome are less likely to be separated than genes that are far apart.separated than genes that are far apart.