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

Answer 1

Answer is  A.

This is an example Mendel’s dihybrid cross.The law of independent assortment of independent assortment. When two individuals heterozygous for both traits (tail color and eyelash length) having genotype (PpLl) are crossed, four types of individuals are produced. The probability of phenotype combinations of offspring is the ratio 9:3:3:1.

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