Question

N the laboratory, you set up an experimental mating between a male and female fruit fly that are both heterozygous (aa) at a locus where the homozygous recessive genotype (aa) is lethal at the early embryo stage. in a large sample of 100 surviving offspring, how many do you expect to have the homozygous dominant (aa) genotype?

Answer 1

Set up the punnett square for the cross. It is Aa x Aa. That can produce four progeny, AA, Aa, aA, and aa. aa will die at the early stages. The surviving progeny will be AA, Aa, or aA. This means 2/3 should be heterozygous and 1/3 will be homozygous dominant. 1/3 *100 = 33 homozygous dominant.