Question

In a test cross, peas of an unknown genotype are crossed withpeas of a known genotype. In this example, smooth peas are theunknown and wrinkled peas are the known (rr). If half of theoffspring from that cross are smooth and half are wrinkled, what isthe genotype of the unknown plant?
A. Incomplete dominance
B. Homozygous dominant: RR
C. Homozygous recessive: rr
D. Heterozygous: Rr
E. The genotype cannot be determined from the informationgiven.

Answer 1

Answer:

D. Heterozygous: Rr

Explanation:

Smooth pea plants can have RR or Rr genotype. It is given that one of the pea plants has recessive rr genotype (wrinkled).

If it is crossed with a heterozygous pea plant (Rr) :

Rr X rr :

   R    r

r  Rr   rr

r  Rr   rr

As evident, half of the offspring will have smooth peas (Rr) and other half will have wrinkled peas (rr). Hence, genotype of unknown plant is Rr.