What is the probability of a white, long-tailed mouse from the cross of a heterozygous black, heterozygous long-tailed mouse with a homozygous recessive white, homozygous recessive short-tailed mouse?
I'm having some trouble with the Punnett Square. The answer is 25%. Thanks!
to do a punnett sq you have to first determine the possible gamete types for each parent. say B=black b=white L=long l=short, where capital and lower case letters represent dominant and recessive traits respectively. The parent that is homozygous recessive for both white fur and short tail has genotype bbll. this means it can only produce one type of gamete: bl. The other parent is heterozygous for both traits so it has genotype BbLl. this means it can produce 4 kinds of gametes: BL Bl bL bl. The genotype the question as for is that of a white long tailed mouse i.e. bbLl (Or bbLL which you will see is impossible given that fact that only one parent has the allele L for long tail).
so a punnet sq would be set up with all possible gamete combinations as follows:
BL Bl bL bl
bl
bl
bl
bl
you can see from above that 4/16 (25%) fertilization events would produce offspring of bblL ie white w long tails.
* i couldn't get the punnett sq to line up correctly but the top row should be shifted a few spaces to the right.
