Genetics: Polydactyly, Fur Color, and Inherited Diseases

4 Polydactyly

is a genetically based human trait which results in extra fingers and toes. With one form of this disorder, the polydactyly allele (P) is dominant to the allele for the normal number of digits (fingers and toes) (p). A polydactyl man that has a father with polydactyly and a mother without polydactyly marries a normal woman with a family of no polydactyl abnormalities. What is the chance of polydactyly in their first child? P P PR 50% chance. 8 for any child, not just. 1st child (odds reset with each child) 5 In guinea pigs, black fur color (B) is dominant over whitefar (b) color. You are given a black guinea pig and a white guinea pig to cross, without knowing their genotypes. Show the two possible crosses and determine for each what percentage of homozygous recessive babies would be produced by the cross. B Bb b Genotypes 2:2 Bb bb b bb Phenotypes b B Bb Genotypes 0:4:0 BB Bb bb Bb b Phenotypes 4:0 White Black 2:2 Black White B Bb Bb 6 A woman with the rare recessive disease phenylketonuria (PKU), which can be treated with a diet of having low levels of the amino acid phenylalanine, was told that it was unlikely her children would inherit PKU because her husband did not have it. However, her first child had PKU. What is the most likely explanation? Assuming this explanation is true, what would be the probability of her second child having PKU? The husband must be a carrier (heterozygous) for PKU P P Pp pp 50% Chance second child Iwill have PKU