Question

Cross Yy and yy. what % of the offspring will be homozygous recessive

Answer 1

The answer is best deduced from a Punnett square:

   Y      y

y  Yy    yy

y  Yy    yy

So the percentage of homozygous recessive (yy) is 2/4 = 50%

Answer 2

We're crossing a heterozygous (Yy) and a homozygous recessive (yy). If we picture that in a punnet square:

    Y      y  

y   Yy    yy  →  In this punnet square we inserted 3 recessive alleles, because                 y   Yy    yy      if we add all of the alleles in our cross, we get three;  and 1 y       dominant allele because in our cross we only have 1 dominant allele.                

- We can see that the homozygous recessive comes up two times, which means the recessive trait gains a 50% predominancy (it comes up 2 times out of 4).

Hope it helped,

BioTeacher101