Question

Suppose that a dominant allele (P) codes for a polka-dot tail and a recessive allele (p) codes for a solid colored tail. In addition, suppose that a dominant allele (L) codes for long eyelashes and a recessive allele (l) codes for short eyelashes. If two individuals heterozygous for both traits (tail color and eyelash length) mate, what's the probability of the phenotypic combinations of the offspring? A. 1:1 ratio (half are polka-dot tails and long eyelashes; half are solid tails and short eyelashes) B. 9:3:3:1 ratio (9 polka-dot tails and long eyelashes, 3 polka-dot tails and short eyelashes, 3 solid tails and short eyelashes, 1 solid tail and short eyelash) C. 9:3:3:1 ratio (9 polka-dot tails and short eyelashes, 3 polka-dot tails and short eyelashes, 3 solid tails and long eyelashes, 1 solid tail and long eyelash) D. 1:1 ratio (half are polka-dot tails and short eyelashes; half are solid tails and long eyelashes)

Answer 1

So, we have two heterozygotous parents, let's call then PL and pl.

if they had children, the children could have either polka-dot tails or not and either long eyelashes, or not, this gives us 4 groups ( so we can reject options A and D which only mention 2 types).


now, there is only one option to have a phenotype which corresponds to recessive allele: that both parents have the recessive allele. So the smallest group will be the one with solid tails and short eye-lashes,

the correct answer is
B. 9:3:3:1 ratio (9 polka-dot tails and long eyelashes, 3 polka-dot tails and short eyelashes, 3 solid tails and short eyelashes, 1 solid tail and short eyelash)