In the Great Dane, the gene that causes the lack of hair, in a homozygous state, leads to the death of the offspring. When two Great Danes with normal phenotypes were crossed, some of the offspring died. When the same male was crossed with another female, there was no death in the offspring. However, when descendants from these two crosses were crossed, the death of the puppies was again observed. Determine the possible genotypes of all crossed individuals and offspring.
If the dominant gene is designated A, recessive a, then the genotype of the male and the first female is Aa, their offspring have genotypes AA and Aa, puppies with genotype aa die; the second female has the AA genotype, and her offspring are AA and Aa, therefore, the death of the puppies is not observed. If, however, two Great Danes with the Aa genotype are crossed with each other, the death of the puppies is again observed, since the homozygotes of aa are cleaved.