4-2 Notes – Understanding Inheritance Chapter 4, Lesson 2

4-2 Notes – Understanding Inheritance

Chapter 4, Lesson 2

Punnett Squares

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

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

Punnett SquaresB = black furb = brown fur

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

b

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

b

b

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

b

b

B b

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

b

b

B b B b

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

b

b

B b B b

bB

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

b

b

B b B b

bB B b

Punnett SquaresB = black furb = brown fur

Female = BB

Male = bb

B B

b

b

B b B b

bB B b

black black

black black

Punnett Squares (5:00)

One-Trait Model

• A cross between two homozygous pea plants: one with yellow seeds (YY) and one with green seeds (yy).

One-Trait Model

• All offspring have the heterozygous genotype (Yy).

• All offspring have the yellow phenotype because Y is dominant to y.

• We call these offspring hybrid because they have one of each type of allele.

Two-Trait Model

Two-Trait Model

• A cross between two heterozygous genotypes (Yy and Yy)

Two-Trait Model

• The offspring would have three different genotypes and two phenotypes.

Two-Trait Model

FF Ff

Ff ff

F = frecklesf = no freckles

freckles freckles

freckles no freckles

• Cross a freckled Dad (Ff) with a freckled Mom (Ff).

Two-Trait Model

Genotypes:

___% are FF

___% are Ff

___% are ffFF Ff

Ff ff

F = frecklesf = no freckles

freckles freckles

freckles no freckles

25

50

25

Two-Trait Model

Phenotypes:

___% have freckles

___% have no freckles

F = frecklesf = no freckles

FF Ff

Ff ff

freckles freckles

freckles no freckles

75

25

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 patterns of inheritance and genetic disorders in families.

Pedigrees

• This pedigree chart shows three generations of a family.

Pedigrees Fill in the key!

Incomplete Dominance

• This is a blend of the parents’ phenotypes.

Codominance

• This is when both alleles can be observed in the phenotype because both are dominant.

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

Codominance

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 blood types: IA, IB, and i.

Multiple Alleles

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

chromosomes - they contain the genes that determine sex (male or female).

Sex-Linked Inheritance• 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.

Sex-Linked Inheritance• A recessive phenotype is observed in a male

when a one-allele gene on his X chromosome has a recessive allele. There is no allele on his Y chromosome to “mask” the recessive allele.

Sex-Linked Inheritance

Sex-Linked InheritanceIn this family, the grandmother’s genome included the color blindness allele.

Sex-Linked Inheritance• Example: red-green

colorblindness

A carrier has one recessive allele and one dominant allele for a trait. They don’t have the trait but can pass it on to offspring.

Polygenic Inheritance

• This is when more than one gene determines the phenotype of a trait.

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

• Examples: hair color, height, skin color

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.

Chris Sutter

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.

Genes and the Environment

Siamese cats have a gene that codes for darker pigments - this gene is more active at low temperatures. Parts of the body that are colder (ears, feet, tail) will develop the darker pigmentation of the Siamese cats.

Punnett squares model the ____ of offspring.

A genotypes

B phenotypes

C genotypes and phenotypes

D genes

4.2 Understanding Inheritance

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

4.2 Understanding Inheritance

How many Y chromosomes do females have?

A 0

B 1

C 2

D 4

4.2 Understanding 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

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

What type of genetic disorder is hemophilia?

A dominant

B X-linked recessive

C codominant

D recessive

SCI 2.d

4-2 Vocab – Understanding Inheritancetext p. 182-190

1. Punnett square

2. pedigree

3. incomplete dominance

4. codominance

5. multiple alleles

6. sex chromosome

7. polygenic inheritance

8. genetic disorder

1. Cross a tall plant (Tt) with a tall plant (Tt).

T = tall, t = short

_____ % tall

_____ % short

Under each genotype, write the correct phenotype.

2. Tall plant (TT) with short plant (tt).

_____ % tall

_____ % short

3. Short plant (tt) with tall plant (Tt).

_____ % tall

_____ % short

4. Tall plant (TT) with tall plant (Tt).

_____ % tall

_____ % short

1. Cross a tall plant (Tt) with a tall plant (Tt).

T = tall, t = short

_75__ % tall

_25__ % short

T t

T

t

TTtall

Tttall

Tttall

ttshort

2. Tall plant (TT) with short plant (tt).

_100__ % tall

_0__ % short

T T

t

t

Tttall

Tttall

Tttall

Tttall

3. Short plant (tt) with tall plant (Tt).

_50__ % tall

_50__ % short

t t

T

t

Tttall

Tttall

ttshort

ttshort

4. Tall plant (TT) with tall plant (Tt).

_100__ % tall

_0__ % short

T T

T

t

TTtall

TTtall

Tttall

Tttall