Question

A. In the space below, place a pedigree chart that can only be interpreted as representing an autosomal dominant trait. Explain why this is so. (6 pts) You may use a written designation. For example

I-1 (affected male X I-2 unaffected female

                                                   

II-1 (affected male II-2 (affected female)

Answer 1

Dominant trait inheritance only requires one allele for the trait to be observed. The dominant allele will repress the expression of recessive allele when present. For the dominant trait to be expressed both the heterozygous as well as homozygous(dominant) will express the trait phenotypically. If the trait is autosomal dominant then one of the parents is required to possess the trait i.e for every affected individual they must have an affected parent. These dominant trait do not skip a generation as even the heterozygous genotype expresses the phenotype.These autosomal dominant traits do not distinguish between the sexes i.e males and females have equal probability of receiving the dominant allele and express it.

in this inheritance one of the parent in the 1st generation has affected or heterozygous genotype take for example Aa while the other parent is recessive for the trait aa. So the next generation offsprings have a probability of 100% chance of expressing the trait irrespective of the gender as the heterozygous dominant allele also can mask the recessive allele. But now for the 3rd generation offsprings the expression of the trait also relies on the other parent. Here in this pedigree chart one individual of the 2nd generation mated with a heterozygous male to give one homozygous dominant as well as heterozygous genotypic offsprings both of which will express the phenotype. For the other individual of 2nd generation he mated with a normal female but as for the inheritance of dominant allele they also give 2 affected offsprings who have heterozygous genotype.