In rabbits, short fur (Y) is dominant over long fur (y) and grey fur (P) is dominant over brown fur (p). The offspring are crossed and the following Punnett square is generated.
Which of the following is the correct genotype marked with the green star?

Question

In rabbits, short fur (Y) is dominant over long fur (y) and grey fur (P) is dominant over brown fur (p). The offspring are crossed and the following Punnett square is generated.
 Which of the following is the correct genotype marked with the green star?

Quizplus · Accepted Answer

According to Mendel's law of independent assortment, alleles of two different genes get sorted into gametes (sex cells) independently of one another. Therefore, the allele one gamete receives for a gene does not influence the allele received for another gene.
In our example, one of the gametes always contains these two alleles - Yp. If we look at the resulting genotypes for the inheritance, we can mark several important conclusions:
There are no genotypes with two recessive "p" alleles.
All genotypes have a recessive "y" allele.
Having these conclusions in mind and knowing one of the parent genotypes (Yp) we can conclude that the other parent genotype has to contain a recessive y allele. This is because the offspring cannot obtain a y allele from the first parent. The genotype in question also must contain a dominant P allele since it is present in all offspring but not in the known parent genotype.
Therefore the genotype we are looking for is yP.

In Rabbits, Short Fur (Y) Is Dominant Over Long Fur