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

Answer 1

Correct answer:
C. 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)

If both parents are heterozygous for both genes, it means that we are crossing two dihybrid organisms. You may start by doing a Punnett squares, one for both characteristics. Attached is the Punnet square, made by me, as it should look in the end. From the Punnet square we take that the genotypes will vary a lot but that it will lead to an offspring that will present the following phenotype proportions:
Polka-dot tail/long eyelashes (both dominant characteristics) - 9/16
Polka-dot tail/short eyelashes (only one dominant characteristic) - 3/16
Solid tail/long eyelashes (only one dominant characteristic) - 3/16
Solid tail/short eyelashes (both recessive characteristics) - 1/16