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 Male parent= bb B B b

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

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

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

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

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

Punnett Square B B B b B b b b B b B b Female parent= BB Male parent= bb B B B b B b b black black b B b B b black 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 Genotypes are FF Ff ff Ff F f F f _____ % FF F= freckles f= no freckles 25 F FF Ff 50 25 f ff Ff

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

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 X- linked 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. Genotypes Phenotypes Genotypes and Phenotypes Genes

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

How many Y chromosomes do females have? 1 2 3

Why are males more likely to be colorblind than females? Maternal inheritance Sex-linked inheritance Polygenic inheritance Incomplete dominance

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

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