Chapter Menu Lesson 1:Foundations of GeneticsFoundations of Genetics Lesson 2:Understanding InheritanceUnderstanding Inheritance Click on a hyperlink

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Lesson 1: Foundations of Genetics

Lesson 2: Understanding Inheritance

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heredity

genetics

dominant

recessive

gene

law of segregation

law of independent assortment

4.1 Foundations of Genetics

allele

phenotype

genotype

homozygous

heterozygous

Early Ideas About Heredity

• Combined genetic material from a sperm and an egg determines the traits or features of an offspring.


• Heredity is the passing of traits from parents to offspring.

Early Ideas About Heredity (cont.)

• The idea of blending inheritance is offspring are a blend of genetic material from both parents.


– The genetic material mixed or blended like colors of paint.

– Over many generations, populations would eventually look alike.

– Blending inheritance cannot explain why some traits skip a generation.

Gregor Mendel and His Experiments

• Gregor Mendel was the first to record evidence that traits are determined by factors passed from parents to offspring.

• Mendel established the basic laws of heredity.

• Genetics is the study of how traits of organisms are passed from parents to offspring.


Mendel’s Experimental Methods

• Mendel conducted breeding experiments by studying seven traits of pea plants and each traits had only two variations.


Controlled Experiments

• Mendel controlled fertilization in the pea plants, allowing him to see how traits pass from one generation to another.


• Mendel allowed some flowers to self-fertilize.

• He also performed cross-fertilization by transferring pollen from one pea flower to another.

Mendel’s Unique Methods

• Used true-breeding plants for each trait—plants that always produce offspring with that trait when they self-pollinate


• Recorded the inheritance of traits for several generations

• Used a mathematical approach

Mendel’s Experimental Results

• Mendel concluded that two factors control each inherited trait.


• When organisms reproduce, each gamete—sperm or egg—contributes one factor for each trait.

Dominant Factors

• A genetic factor that blocks another genetic factor is called dominant.


• A dominant trait is observed when offspring have one or two dominant factors.

Recessive Factors

• A genetic factor that is hidden by the presence of a dominant factor is recessive.


• A recessive trait can be observed only when two recessive genetic factors are present in offspring.

Mendel’s Laws of Heredity

• Law of segregation: the two factors for each trait segregate—separate from each other—during meiosis when gametes form


• Law of independent assortment: the factors for one trait separate independently of how factors for other traits separate

Modern Definitions of Mendel’s Ideas

• Mendel did not know about DNA or how cells reproduce, but his ideas about inheritance are still true today.


Genes and Alleles

• A gene is a section of DNA that has information about a trait in an organism.


• Each form of a gene with different information is called an allele.

Genes and Alleles (cont.)


Phenotype and Genotype

• The observable traits and all characteristics of an organism make up the organism’s phenotype.


• The alleles that make up an organism is the organism’s genotype.

• The alleles of a particular gene is that gene’s genotype.

Homozygous and Heterozygous Genotypes

• Because eukaryotes have pairs of chromosomes, a genotype for a gene has two alleles.


• If the two alleles have the same information, the genotype is homozygous.

• If the two alleles have different information, the genotype is heterozygous.

Homozygous and Heterozygous Genotypes (cont.)


Law of Segregation Explained• The movement of chromosomes during meiosis

explains Mendel’s law of segregation.

– Each set of chromatids separates into different gametes during meiosis II.

– Each gamete receives only one allele.


Law of Segregation Explained (cont.)


Law of Independent Assortment Explained

• The daughter cells produced by meiosis receive only one chromosome from each pair of homologous chromosomes.

– A daughter cell might receive the A or a chromosome from pair 1 and the B or b chromosome from pair 2.

– This results in four possible allele combinations for two homologous pairs of chromosomes.


Law of Independent Assortment Explained (cont.)


Importance of Mendel’s Genetic Studies

• In the 1860s, no one knew about chromosomes or meiosis so it was hard to understand Mendel’s discoveries.

• All the research of modern genetics is based on Mendel’s conclusions from his work with pea plants.


Lesson 1 Review

What is the passing of traits from parents to offspring called?

A inheritance

B genetics

C heredity

D allele


Lesson 1 Review

What are the alleles that make up an organism called?

A genes

B genotype

C phenotype

D factors


Lesson 1 Review

If two alleles for a gene have the same information, what kind of genotype does that gene have?

A homologous

B recessive

C heterozygous

D homozygous


End of Lesson 1

Punnett square

pedigree

incomplete dominance

codominance

multiple alleles

sex chromosomes

polygenic inheritance

genetic disorder

4.2 Understanding Inheritance

Modeling Inheritance

– Punnett square

– pedigree

• Two tools can be used to identify and predict traits among genetically related individuals.


Heredity

Punnett Squares

• If the genotypes of the parents are known, the genotypes and phenotypes of the offspring can be predicted.

• A Punnett square is a model used to predict possible genotypes and phenotypes of offspring.


One-Trait Model• The Punnett square shows the possible offspring of a cross between two true-breeding pea plants—one

with yellow seeds and one with green.


One-Trait Model (cont.)

– The phenotype will be yellow seeds because Y is dominant to y.

– The only possible genotype for hybrid offspring is heterozygous—Yy.


One-Trait Model (cont.)


Two-Trait Model• The possible offspring of two heterozygous genotypes—Yy and Yy—would have

three different genotypes and two phenotypes.


Pedigrees• All the genetically related members of a family are part

of a family tree.


• A pedigree shows genetic traits that were inherited by members of a family tree.

• Pedigrees are important tools for tracking complex pattern of inheritance and genetic disorders in families.

Pedigrees (cont.)


A pedigree chart that shows three generations of a family.

Types of Dominance• Alleles show incomplete dominance when they produce

a phenotype that is a blend of the parents’ phenotypes.

• When both alleles can be observed in the phenotype, the interaction is called codominance.


– The human blood type AB is an example of codominance.

Multiple Alleles• Some genes have more than two alleles, or multiple

alleles.

• The human ABO blood group is determined by multiple alleles as well as codominance.

• There are three different alleles for the ABO blood type—IA, IB, and i.


Multiple Alleles (cont.)


Sex-Linked Inheritance• Chromosomes X and Y are the sex chromosomes—

they contain the genes that determine gender or sex.


• Except for sperm and eggs, each cell in a male has an X and a Y chromosome, and each cell in a female has two X chromosomes.

• A recessive phenotype is observed in a male when a one-allele gene on his X chromosome has a recessive allele.

Sex-Linked Inheritance (cont.)


In this family, the grandmother’s genome included the color blindness allele.

Polygenic Inheritance• Polygenic inheritance is when multiple genes

determine the phenotype of a trait.


• Many phenotypes are possible when possible when polygenic inheritance determines a trait.

Maternal Inheritance• Humans inherit mitochondrial genes only from their

mothers.


• Inheritance of traits related to the mitochondria can be traced from grandmother to grandchildren.

How are the traits of parents inherited and expressed in offspring?

Human Genetic Disorders• If a change occurs in a gene, the organism with the

mutation may not be able to function as it should.


• An inherited mutation can result in a phenotype called a genetic disorder.

Human Genetic Disorders (cont.)


Genes and the Environment

• An organism’s environment can affect its phenotype.

– Genes affect heart disease, but so do diet and exercise.

– Genes affect skin color, but so does exposure to sunlight.


Lesson 2 Review

Punnett squares model the ____ of offspring.

A genotypes

B phenotypes

C genotypes and phenotypes

D genes


Lesson 2 Review

What is the term for when alleles produce a phenotype that is a blend of the parents’ phenotypes?

A incomplete dominance

B codominance

C multiple alleles

D polygenic inheritance


Lesson 2 Review

How many Y chromosomes do females have?

A 0

B 1

C 2

D 4


End of Lesson 2

Chapter Assessment

California Standards Practice

Concepts in Motion

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What is the term for the idea that offspring are a blend of genetic material from both parents?

A polygenic inheritance

B sex-linked inheritance

C maternal inheritance

D blending inheritance

Chapter Assessment 1

What type of alleles can only be observed in the phenotype when they are present as a homozygous genotype?

A dominant

B recessive

C inherited

D heterozygous


What is the term for the idea that inheritance of one trait is not influenced by inheritance of another trait?

A law of independent assortment

B law of heredity

C law of segregation

D maternal inheritance


What is a good example of a trait that is determined by multiple alleles?

A color of camellia flowers

B human AB blood type

C color blindness

D human ABO blood group


Why are male humans more likely to be color-blind than females?

A maternal inheritance

B sex-linked inheritance

C polygenic inheritance

D incomplete dominance


Which pea trait did Mendel not study?

A seed color

B pod color

C flower position

D flower shape

CA Standards Practice 1

SCI 2.c

If two plants with genotypes Mm are crossed, what percent of the offspring will have phenotype M?

A 0%

B 25%

C 75%

D 100%


SCI 2.d

What is the term for when more than one gene determine a trait?

A incomplete dominance

B multiple alleles

C polygenic inheritance

D sex-linked inheritance


SCI 2.c, 2.d

Which does NOT describe Mendel’s experiments?

A Mendel observed several generations of plants.

B Mendel chose pea plants because they reproduce quickly.

C Mendel counted small numbers of offspring.

D Mendel used true-breeding plants.


SCI 2.d

What type of genetic disorder is hemophilia?

A dominant

B X-linked recessive

C codominant

D recessive


SCI 2.d

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Concepts in Motion 2

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