Question

Suppose that a dominant allele (P) codes for a polka-dot tail and a recessive allele (p) codes for a solid colored tail. If two heterozygous individuals with polka-dot tails mate, what's the probability of the phenotype and genotype combinations of the offspring? A. 75 percent chance of a polka-dot tail and 25 percent chance of a solid colored tail (75 percent Pp; 25 percent pp) B. 75 percent chance of a polka-dot tail and 25 percent chance of a solid colored tail C. 25 percent chance of a polka-dot tail and 75 percent chance of a solid colored tail D. 50 percent chance of a polka-dot tail and 50 percent chance of a solid colored tail

Answer 1

The correct answer is B. This question relates to using a punnet square to determine the genotypes of the offspring. Two heterozygous parents expressing a polka-dot tale must have genotype Pp each.

Using a punnet square, this will produce 4 possible genotypes in equal probability:
PP - polka dot
Pp - polka dot
Pp - polka dot
pp - solid tale

Therefore there is a 75% change of getting polka dots in the offspring, and a 25% chance of solid tale.

A. is an incorrect answer because only 50% of offspring will be type Pp, another 25% will be expressing double dominant alleles for P as PP, which will still express polka dots.