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. 9:3:3:1 ratio (9 polka-dot tails and short eyelashes, 3 polka-dot tails and long eyelashes, 3 solid tails and short eyelashes, 1 solid tail and long eyelash)
B. 1:1 ratio (half are polka-dot tails and long eyelashes; half are solid tails and short eyelashes)
C. 1:1 ratio (half are polka-dot tails and short eyelashes; half are solid tails and long eyelashes)
D. 9:3:3:1 ratio (9 polka-dot tails and long eyelashes, 3 polka-dot tails and short eyelashes, 3 solid tails and long eyelashes, 1 solid tail and short eyelash)
Please help♥

Answer 1

When you put that into a Punnett square you first use the FOIL method because this is a dihybrid case where two traits are considered. This will be the resulting Punnett square:


           PL      Pl        pL       pl

PL    PPLL   PPLl   PpLL   PpLl

Pl     PPLl    PPll     PpLl    Ppll

pL    PpLL    PpLl    ppLL   ppLl

pl     PpLl     Ppll      ppLl    ppll

Now based on the Punnett square above, you can get the ratio. Remember that the dominant trait will always be expressed when you count phenotype combinations so as long as there is a capital letter in the combination, it will always be the one expressed. 

So there are 9 polka dot, long eyelashes(PL), 3 polka dot, short eyelashes (Pl), 3 solid color, long eyelashes (pL), 1 solid short eyelashes(pl).

So your answer is D. 9:3:3:1 ratio