Whether a pea seed is round or wrinkled is due to a single Mendelian gene, with round seeds being dominant to wrinkled seeds.In the progeny of a test cross, _______ of 80 seeds should be round if the unknown round-seeded individual being tested is heterozygous.
A) 0
B) 20
C) 40
D) 60
E) 80

Question

Quizplus · Accepted Answer

If the unknown round-seeded individual being tested is heterozygous, then it can be represented as Rr (where R represents round seed allele and r represents wrinkled seed allele). In a test cross, the individual is crossed with a homozygous recessive individual (rr). The possible gametes for Rr individual are R and r, while for the rr individual it is only r. Therefore, the possible offspring will be Rr and rr in a 1:1 ratio. Since round seeds are dominant, only individuals with at least one R allele will have round seeds. Therefore, out of the 80 possible offspring, 40 will have round seeds (Rr) and 40 will have wrinkled seeds (rr). Thus, the answer is (C) 40.

Whether a Pea Seed Is Round or Wrinkled Is Due