Understanding Inheritance Punnett Squares A Punnett Square is

Understanding Inheritance

Punnett Squares • A Punnett Square is a model that can be used to predict the possible genotypes and phenotypes of the offspring of two parents.

Punnett Square • B= black fur • b= brown fur

Punnett Square Female parent= BB Male parent= bb B

Punnett Square Female parent= BB Male parent= bb B B

Punnett Square Female parent= BB B b Male parent= bb B

Punnett Square Female parent= BB B b Male parent= bb b B

Punnett Square Female parent= BB B b Male parent= bb b Bb B

Punnett Square Female parent= BB b Male parent= bb b B B Bb Bb

Punnett Square Female parent= BB B B b Bb Bb Male parent= bb

Punnett Square Female parent= BB B B b Bb Bb Male parent= bb

Punnett Square Female parent= BB B B b Bb black b Bb Bb Male parent= bb black

Punnett Square • A cross between two homozygous pea plants • One with yellow seeds (YY) • One with green seeds (yy)

Punnett Squares • All offspring have the heterozygous genotype • All offspring have the yellow phenotype • These offspring are called hybrids because they have one of each allele

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

Punnett Squares • The offspring would have 3 different genotypes and 2 different phenotypes.

Punnett Squares • Cross a freckled Dad (Ff) with a freckled Mom (Ff) • F= freckles • f= no freckles

Punnett Squares F F f FF Ff ff Genotypes are 25 % FF _____ 50 % Ff _____ 25 _____ % ff F= freckles f= no freckles

Punnett Squares F f F FF Ff 75 % Freckles _____ 25 % No freckles _____ f Ff ff F= freckles f= no freckles Phenotypes are

Incomplete Dominance • Occurs in a heterozygous individual when the dominant allele is not completely expressed over the recessive allele • Results in a blend of the two parent phenotypes

Incomplete Dominance • Common in: • Flower color • Eye color • Skin color

Codominance • Occurs when both alleles can be observed because both are dominant. Example: Cow color RR= red WW= white RW= roan (red and white)

Codominance Example: Horse color GG= gray WW= white GW= Apaloosa (white with gray spots)

Codominance • The human blood type AB is a codominant trait because blood type A and B are both dominant.

Multiple Alleles • Some genes are controlled by more than two alleles. • Human blood type is determined by 3 different alleles • IA= Type A blood (dominant) • IB= Type B blood (dominant) • i= type O blood (recessive)

Sex-Linked Inheritance • One pair of human chromosomes determines sex. • Two X chromosomes: female • One X and one Y chromosome: male

Sex-Linked Inheritance • Some genes are carried on the X chromosome. • If a male gets a recessive allele of an Xlinked gene, then he will have the recessive trait (because he has no allele on the Y chromosome to “hide” the recessive trait).

Sex-Linked Inheritance • Common sex-linked traits • Hemophilia • Color blindness

Sex-Linked Inheritance • A carrier has one recessive allele. • They don’t have the trait but they can pass on the trait.

Polygenic Inheritance • When more than one gene determines the phenotype of a trait • Many phenotypes are possible in polygenic inheritance • Examples in humans: eye color, skin color, height

Genetic Disorders • If a change occurs in a gene, it is called a mutation. • Inherited mutations can cause a genetic disorder.

Genes and the Environment • An organism’s environment can affect its phenotype • Genes affect heart disease, but so does diet and exercise • Genes affect skin color, but so does exposure to sunlight

Punnett squares model the ___ of offspring. A. Genotypes B. Phenotypes C. Genotypes and Phenotypes D. Genes

What is it called when alleles produce a phenotype that is a blend of the parents’ phenotypes? A. Incomplete dominance B. Codominance C. Multiple alleles D. Polygenic inheritance

How many Y chromosomes do females have? A. 0 B. 1 C. 2 D. 3

Why are males more likely to be colorblind than females? A. Maternal inheritance B. Sex-linked inheritance C. Polygenic inheritance D. Incomplete dominance

If two plants with genotype Mm are crossed, what % of the offspring will have the dominant phenotype? A. 0% B. 25% C. 50% D. 75%

What is it called when more than one gene determines a trait? A. Incomplete dominance B. Codominance C. Polygenic Inheritance D. Sex-linked inheritance