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Chapter Eleven Lecture- Intro to Genetics
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biology
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11-1 The Work of Gregor Mendel11-1 The Work of Gregor Mendel
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Gregor Mendel’s Peas
Genetics is the scientific study of heredity.Gregor Mendel was an Austrian monk. His work was important to the understanding of heredity.Mendel carried out his work with ordinary garden peas.
Gregor Mendel’s Peas
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Gregor Mendel’s Peas
Mendel knew that • the male part of
each flower produces pollen, (containing sperm).
• the female part of the flower produces egg cells.
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Gregor Mendel’s Peas
During sexual reproduction, sperm and egg cells join in a process called fertilization.
Fertilization- sperm and egg join to produce a new cell.
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Gregor Mendel’s Peas
Pea flowers are self-pollinating.Sperm cells in pollen fertilize the egg cells in the same flower. The seeds that are produced by self-pollination inherit all of their characteristics from the single plant that bore them.
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Gregor Mendel’s Peas
Mendel had true-breeding pea plants.
True-breeding plants, if allowed to self-pollinate, produce offspring identical to themselves.
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Gregor Mendel’s Peas
Mendel wanted to produce seeds by joining male and female reproductive cells from two different plants.He cut away the pollen-bearing male parts of the plant and dusted the plant’s flower with pollen from another plant.
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Gregor Mendel’s Peas
This process is called cross-pollination.
Cross-pollination produces seeds that have two different parents.
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Genes and Dominance
A trait is a specific characteristic that varies from one individual to another.
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Genes and Dominance
Mendel studied seven pea plant traits, each with two contrasting characters.He crossed plants with each of the seven contrasting characters and studied their offspring.
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Genes and Dominance
Each original pair of plants is the P (parental) generation. The offspring are called the F1, or “first filial,” generation.
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Genes and Dominance
The offspring of crosses between parents with different traits are called hybrids.The F1 hybrid plants all had the character of only one of the parents.
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Mendel’s F1 Crosses on Pea Plants
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Mendel’s Seven F1 Crosses on Pea Plants
Mendel’s F1 Crosses on Pea Plants
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Genes and Dominance
Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next. = genes!
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Genes and Dominance
Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.
The different forms of a gene are called alleles. Mendel’s second conclusion is called the principle of dominance.
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Genes and Dominance
The principle of dominance states that some alleles are dominant and others are recessive.
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Genes and Dominance
An organism with a dominant allele for a trait will always exhibit that form of the trait.An organism with the recessive allele for a trait will exhibit that form only when the dominant allele for that trait is not present.
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Genes and Dominance
Pink x white = all pink
Pink is dominant alleleWhite is recessive allele
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SegregationSegregationMendel crossed the F1 generation with itself to produce the F2 (second filial) generation.The traits controlled by recessive alleles reappeared in one fourth of the F2 plants.
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Mendel's F2 GenerationP Generation F1 Generation
Tall Tall Tall Tall Tall TallShort Short
F2 Generation
Segregation
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Segregation
Mendel assumed that the dominant allele masks the recessive allele in the F1 generation.
The trait controlled by the recessive allele showed up in some of the F2 plants.
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Segregation
The reappearance of the recessive trait showed that the allele for shortness had been separated, or segregated, from the allele for tallness.
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Segregation
Mendel suggested that the alleles segregate from each other during the formation of the sex cells, or gametes.
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SegregationWhen each F1 plant flowers and produces gametes, the two alleles segregate from each other so that each gamete carries only a single copy of each gene. Therefore, each F1 plant produces two types of gametes—those with the allele for tallness, and those with the allele for shortness.
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Segregation
Alleles separate during gamete formation.
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11-2 Probability and Punnett Squares
11-2 Probability and Punnett Squares
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Genetics and Probability
The likelihood that a particular event will occur is called probability.Probability can be used to predict the outcomes of genetic crosses.
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Punnett Squares
Punnett squares are diagrams used to predict and compare the genetic variations that will result from a cross.
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A capital letter represents the dominant allele.A lowercase letter represents the recessive allele.In this example, T = tallt = short
Punnett Squares
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Punnett Squares
Gametes produced by each parent are shown along the top and left side.
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Punnett Squares
Possible gene combinations for the offspring appear in the four boxes.
Punnett Squares
Organisms that have two identical alleles for a particular trait are said to be homozygous. Organisms that have two different alleles for the same trait are heterozygous.
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Punnett Squares
Homozygous organisms are true-breeding for a particular trait. Heterozygous organisms are hybrid for a particular trait.
Punnett Squares
Offspring have the same phenotype if they show the same trait. Offspring have the same genotype if they have the same genetic makeup (alleles).
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Punnett Squares
The plants have different genotypes (TT and Tt), but they have the same phenotype (tall).
TTHomozygous
TtHeterozygousActive art
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Probability and Segregation Probability and
Segregation•One fourth (1/4) of the
F2 plants have two alleles for tallness (TT).
•2/4 or 1/2 have one allele for tall (T), and one for short (t).
•One fourth (1/4) of the F2 have two alleles for short (tt).
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Probability and Segregation
The ratio of plants showing the dominant phenotype (TT or Tt genotype) to those showing the recessive phenotype(tt genotype) plants is 3:1.The predicted ratio showed up in Mendel’s experiments indicating that segregation did occur.
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Probabilities Predict Averages
Probabilities Predict Averages•Probabilities predict the average
outcome of a large number of events.•Probability cannot predict the precise
outcome of an individual event.• In genetics, the larger the number of
offspring, the closer the resulting numbers will get to expected values.
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11-3 Exploring Mendelian Genetics
11–3 Exploring Mendelian Genetics
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Independent Assortment•To determine if the segregation of one
pair of alleles affects the segregation of another pair of alleles, Mendel performed a two-factor cross.
Independent Assortment
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Independent Assortment
The Two-Factor Cross: F1 •Mendel crossed true-breeding plants that produced round yellow peas (genotype RRYY) with true-breeding plants that produced wrinkled green peas (genotype rryy).•All of the F1 offspring produced round yellow peas (RrYy).
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Independent Assortment
The alleles for round (R) and yellow (Y) are dominant over the alleles for wrinkled (r) and green (y).
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Independent Assortment
The Two-Factor Cross: F2
•Mendel crossed the heterozygous F1 plants (RrYy) with each other to determine if the alleles would segregate from each other in the F2 generation.
• RrYy × RrYy
Independent Assortment
For a two-factor F1 hybrid cross, the Punnett square predicts a 9 : 3 : 3 :1 ratio in the F2 generation.
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In Mendel’s experiment, the F2 generation produced the following:•9 seeds that were round and yellow•3 seeds that were round and green•3 seeds that were wrinkled and yellow•1 seed that was wrinkled and green
Independent Assortment
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The principle of independent assortment states that alleles for different traits can segregate independently during the formation of gametes.Genes that segregate independently do not influence each other's inheritance.
Independent Assortment
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Mendel's experimental results were very close to the 9 : 3 : 3 : 1 ratio predicted by the Punnett square.Mendel had discovered the principle of independent assortment.
Independent Assortment
Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms.
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A Summary of Mendel's Principles
A Summary of Mendel's Principles
•Genes are passed from parents to their offspring. • If two or more forms (alleles) of the
gene for a single trait exist, some forms of the gene may be dominant and others may be recessive.
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• In most sexually reproducing organisms, each adult has two copies of each gene. These genes are segregated from each other when gametes are formed.
•The alleles for different genes usually segregate independently of one another.
A Summary of Mendel's Principles
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Beyond Dominant and Recessive Alleles
Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.
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Beyond Dominant and Recessive Alleles
Incomplete Dominance •When one allele is not completely
dominant over another it is called incomplete dominance.
•In incomplete dominance, the heterozygous phenotype is between the two homozygous phenotypes.
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A cross between red (RR) and white (WW) four o’clock plants produces pink-colored flowers (RW).
Beyond Dominant and Recessive Alleles
WW
RR
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Beyond Dominant and Recessive Alleles
•In codominance, both alleles contribute to the phenotype (like spots!).
• In certain varieties of chicken, the allele for black feathers is codominant with the allele for white feathers.
•Heterozygous chickens are speckled with both black and white feathers. The black and white colors do not blend to form a new color, but appear separately.
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Beyond Dominant and
Multiple Alleles •Genes that are controlled by more than
two alleles are said to have multiple alleles.
•An individual can’t have more than two alleles. However, more than two possible alleles can exist in a population.
•A rabbit's coat color is determined by a single gene that has at least four different alleles.
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Beyond Dominant and Recessive Alleles
Different combinations of alleles result in the colors shown here.
Full color: CC, Ccch, Cch, or CcChinchilla: cchch, cchcch, or cchcHimalayan: chc, or chch AIbino: cc
KEY
C = full color; dominant to all other alleles
cch = chinchilla; partial defect in pigmentation; dominant to ch and c alleles
ch = Himalayan; color in certain parts of the body; dominant to c allele
c = albino; no color; recessive to all other alleles
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Beyond Dominant and Recessive Alleles
•Polygenic Traits •Traits controlled by two or more genes
are said to be polygenic traits.•Skin color in humans is a polygenic trait
controlled by more than four different genes.
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Applying Mendel's Principles
Applying Mendel's Principles•Thomas Hunt Morgan used fruit flies to
advance the study of genetics.•Morgan and others tested Mendel’s
principles and learned that they applied to other organisms as well as plants.
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Applying Mendel's Principles
Mendel’s principles can be used to study inheritance of human traits and to calculate the probability of certain traits appearing in the next generation.
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Genetics and the Environment
Genetics and the Environment•Characteristics of any organism are
determined by the interaction between genes and the environment.
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11-4 Meiosis11-4 Meiosis
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Each organism must inherit a single copy of every gene from each of its “parents.”Gametes are formed by a process that separates the two sets of genes so that each gamete ends up with just one set.
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Chromosome Number
Chromosome NumberOrganisms have different numbers of chromosomes.A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent.
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Chromosome Number
Chromosomes come in homologous pairs. Homologous chromosomes contain genes for the same traits.Each of the 4 chromosomes that came from the male parent has a homologous chromosome from the female parent.
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Chromosome Number
A cell that contains both sets of homologous chromosomes is said to be diploid (2N).The number of chromosomes in a diploid cell is sometimes represented by the symbol 2N.For Drosophila, the diploid number is 8, which can be written as 2N=8.
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Chromosome Number
The gametes of sexually reproducing organisms contain only a single set of chromosomes, and therefore only a single set of genes.
Gametes are haploid (N), with only one set of the homologous chromosomes.Haploid cells are represented by the symbol N.For Drosophila, the haploid number is 4, which can be written as N=4.
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Phases of Meiosis
Meiosis is a process of division in which the number of chromosomes per cell is cut in half.Diploid = 2 sets of each geneHaploid = half = one of each gene
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•Meiosis involves two divisions, meiosis I and meiosis II.
•The diploid cell that enters meiosis becomes 4 haploid cells.
Phases of Meiosis
Movie
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Phases of Meiosis
Meiosis I
Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis
Interphase IMeiosis I
Movie
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Phases of Meiosis
Cells undergo a round of DNA replication, forming duplicate chromosomes.
Interphase I
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Phases of Meiosis
During prophase of meiosis 1, each chromosome pairs with its corresponding homologous chromosome to form a tetrad.There are 4 chromatids in a tetrad.
MEIOSIS I Prophase I
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Phases of Meiosis
•When tetrads form in prophase I, they exchange portions of their chromatids in a process called crossing over.
• Crossing-over produces new combinations of alleles.
Movie
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Phases of Meiosis
Spindle fibers attach to the chromosomes.
MEIOSIS I Metaphase I
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Phases of Meiosis
MEIOSIS I Anaphase IThe fibers pull the
homologous chromosomes toward opposite ends of the cell.
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Phases of Meiosis
MEIOSIS I Telophase I and Cytokinesis
Nuclear membranes form. The cell separates into two cells.The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the parent cell.
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Phases of Meiosis
Meiosis II•The two cells produced by meiosis I
now enter a second meiotic division.•Unlike meiosis I, neither cell goes
through chromosome replication.•Each of the cell’s chromosomes has 2
chromatids.
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Phases of Meiosis
Meiosis II
Telophase II and Cytokinesis
Prophase IIMetaphase II Anaphase IITelophase I and
Cytokinesis IMeiosis II
Movie
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Phases of Meiosis
Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell.
MEIOSIS IIProphase II
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Phases of Meiosis
The chromosomes line up in the center of cell.
MEIOSIS II Metaphase II
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Phases of Meiosis
The sister chromatids separate and move toward opposite ends of the cell.
MEIOSIS II Anaphase II
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Phases of Meiosis
Meiosis II results in four haploid (N) daughter cells.
MEIOSIS II Telophase II and Cytokinesis
Active art
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Gamete Formation
Gamete Formation
In male animals, meiosis results in four equal-sized gametes called sperm.
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Gamete Formation
In many female animals, one egg and 3 polar bodies result from meiosis. The three cells, called polar bodies, are usually not involved in reproduction.
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Comparing Mitosis and Meiosis
Comparing Mitosis and Meiosis
Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different haploid cells.
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Comparing Mitosis and Meiosis
Mitosis•Cells produced by mitosis have the
same number of chromosomes and alleles as the original cell.
•Mitosis allows an organism to grow and replace cells.
•Some organisms reproduce asexually by mitosis.
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Comparing Mitosis and Meiosis
Meiosis•Cells produced by meiosis have half the
number of chromosomes as the parent cell.•These cells are genetically different from the
diploid cell and from each other.
•Meiosis is how sexually-reproducing organisms produce gametes.
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Gene Linkage
Thomas Hunt Morgan researched the genetics of fruit flies because they had many offspring in a short time.
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11-5 Linkage and Gene Maps
11-5 Linkage and Gene Maps
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Gene Linkage
Gene Linkage•Thomas Hunt Morgan’s research on fruit
flies led him to the principle of linkage.•Morgan discovered that many of the
more than 50 Drosophila genes he had identified appeared to be “linked” together.
•They seemed to violate the principle of independent assortment.
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Morgan and his associates grouped the linked genes into four linkage groups.Each linkage group assorted independently but all the genes in one group were inherited together.
Each chromosome is actually a group of linked genes ( a linkage group).
Gene Linkage
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Gene Linkage
Morgan concluded that Mendel’s principle of independent assortment still holds true. Chromosomes assort independently, not individual genes.Mendel did not observe gene linkage because the genes he studied happened to be on different chromosomes.
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Gene Maps
Gene Maps
•Crossing-over during meiosis sometimes separates genes that had been on the same chromosomes onto homologous chromosomes.
•Crossover events can separate linked genes and produce new combinations of alleles.
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Alfred Sturtevant, a student of Morgan, reasoned that the farther apart two linked genes are, the more likely they are to be separated due to crossover.Recombination frequencies can be used to determine the distance between genes.
Gene Maps
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Sturtevant created a gene map of a Drosophila chromosome. A gene map shows the relative locations of each known gene on a chromosome.
Gene Maps
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If two genes are close together, the recombination frequency between them should be low, since crossovers are rare.If they are far apart, recombination rates between them should be high.
Gene Maps
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Gene Maps
Aristaless (no bristles on antenna)
Chromosome 2Exact location on chromosome
13.0 Dumpy wing
0.0
48.5 Black body
54.5 Purple eye
67.0 Vestigial (small) wing
99.2 Arc (bent wings)
107.0 Speck wing
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Chromosome 2Exact location on chromosome
1.3 Star eye
31.0 Dachs (short legs)
51.0 Reduced bristles
55.0 Light eye
75.5 Curved wing
104.5 Brown eye
Gene Maps
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11-1
Gametes are also known as
a. genes.
b. sex cells.
c. alleles.
d. hybrids.
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11-1
The offspring of crosses between parents with different traits are called
a. alleles.
b. hybrids.
c. gametes.
d. dominant.
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11-1
In a cross of a true-breeding tall pea plant with a true-breeding short pea plant, the F1 generation consists of
a. all short plants.
b. all tall plants.
c. half tall plants and half short plants.
d. all plants of intermediate height.
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11-1
If a particular form of a trait is always present when the allele controlling it is present, then the allele must be
a. mixed.
b. recessive.
c. hybrid.
d. dominant.
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11-2
Probability can be used to predict
a. average outcome of many events.
b. precise outcome of any event.
c. how many offspring a cross will produce.
d. which organisms will mate with each other.
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11-2
Compared to 4 flips of a coin, 400 flips of the coin is
a. more likely to produce about 50% heads and 50% tails.
b. less likely to produce about 50% heads and 50% tails.
c. guaranteed to produce exactly 50% heads and 50% tails.
d. equally likely to produce about 50% heads and 50% tails.
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11-2
Organisms that have two different alleles for a particular trait are said to be
a. hybrid.
b. heterozygous.
c. homozygous.
d. recessive.
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11-2
Two F1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall?
a. 100%
b. 50%
c. 0%
d. 25%
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11-2
The Punnett square allows you to predict
a. only the phenotypes of the offspring from a cross.
b. only the genotypes of the offspring from a cross.
c. both the genotypes and the phenotypes from a cross.
d. neither the genotypes nor the phenotypes from a cross.
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11–3
In a cross involving two pea plant traits, observation of a 9 : 3 : 3 : 1 ratio in the F2 generation is evidence for
a. the two traits being inherited together.
b. an outcome that depends on the sex of the parent plants.
c. the two traits being inherited independently of each other.
d. multiple genes being responsible for each trait.
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11–3
In four o'clock flowers, the alleles for red flowers and white flowers show incomplete dominance. Heterozygous four o'clock plants have
a. pink flowers.
b. white flowers.
c. half white flowers and half red flowers.
d. red flowers.
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11–3
A white male horse and a tan female horse produce an offspring that has large areas of white coat and large areas of tan coat. This is an example of
a. incomplete dominance.
b. multiple alleles.
c. codominance.
d. a polygenic trait.
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11–3
Mendel's principles apply to
a. pea plants only.
b. fruit flies only.
c. all organisms.
d. only plants and animals.
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11-4
If the body cells of humans contain 46 chromosomes, a single sperm cell should have
a. 46 chromosomes.
b. 23 chromosomes.
c. 92 chromosomes.
d. between 23 and 46 chromosomes.
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11-4
During meiosis, the number of chromosomes per cell is cut in half through the separation of
a. daughter cells.
b. homologous chromosomes.
c. gametes.
d. chromatids.
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11-4
The formation of a tetrad occurs during
a. anaphase I.
b. metaphase II.
c. prophase I.
d. prophase II.
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11-4
In many female animals, meiosis results in the production of
a. only 1 egg.
b. 1 egg and 3 polar bodies.
c. 4 eggs.
d. 1 egg and 2 polar bodies.
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11-4
Compared to egg cells formed during meiosis, daughter cells formed during mitosis are
a. genetically different, while eggs are genetically identical.
b. genetically different, just as egg cells are.
c. genetically identical, just as egg cells are.
d. genetically identical, while egg cells are genetically different.
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11-5
According to Mendel's principle of independent assortment, the factors that assort independently are the
a. genes.
b. chromosomes.
c. chromatids.
d. gametes.
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11-5
Linkage maps can be produced because the farther apart two genes are on a chromosome,
a. the less likely they are to assort independently.
b. the more likely they are to be linked.
c. the more likely they are to be separated by a crossover.
d. the less likely they are to be separated by a crossover.
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11-5
If two genes are close together on the same chromosome, they are more likely to
a. behave as though they are linked.
b. behave independently.
c. move to different chromosomes.
d. belong to different linkage groups.
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