Pedigrees & More Genetics

Pedigree Male Female Heterozygous Shows trait

1/2 1/2 2/2 x 1 = 1/2 (1) Aa aa Probabilities Child will have recessive trait? aa Chance of “a” allele from dad? Chance of “a” allele from mom? Total 1/2 x 1 = 1/2 1/2 2/2 (1)

Recessive characteristics Inheritance pattern Trait tends to skip generations

Dominant characteristics Trait does not skip generations Occurs frequently within a family

Pedigree Analysis

Sex linked characteristics Tend to occur more in males than in females Color-blindness Hemophilia

X-linked Recessives: More commonly seen in Males Why? Males only need one recessive allele to see trait. E.g. Color-blindness XcY = colorblind male XcXc = colorblind female XcX = carrier female

A woman with normal vision whose father was colorblind marries a colorblind male. What percent of the couple’s sons will be colorblind? All 75% 50% 25%

A woman with normal vision whose father was colorblind marries a colorblind male. What percent of the couple’s sons will be colorblind? All 75% 50% 25% Xc X XcXc XcX Y XcY XY

Incomplete Dominance

Codominance &Multiple Alleles

Epistasis A gene at one locus alters the expression of a gene at another locus. Example: Black coat (B) is dominant to brown (b) Pigment color (C) is dominant to no pigment color (c)

Polygenic Traits Additive effect of multiple genes on a single phenotype Results in normal distribution Examples: skin color, height

Effect of Environment on Phenotype More acidic soil Less acidic soil

Pleiotropic Effects