Question

Considering the Mendelian traits tall (D) versus dwarf (d) and violet (W) versus white (w), consider the crosses below and determine the genotypes of the parental plants by analyzing the phenotypes of the offspring.
Parental Plants Offspring
tall, violet x dwarf, white 1/4 tall, violet
1/4 tall, white
1/4 dwarf, violet
1/4 dwarf, white
Select all that apply.

Select all that apply.

a)DDWW x DdWw
b)DdWw x ddww
c)Ddww x ddWw
d)DdWw x DdWw
DDWw x ddww

Answer 1

Use a Punnet square to answer the question

Answer 2

Based on the setting of the question, a parental plant of the dwarf/white phenotype can only have the recessive genotype of ddww (Only b or e plausible). Thereby the cross is considered a test cross, in which the phenotype of the offspring depends solely on the alleles from the non-recessive parent, in this case, the tall and violet plant (Genotype DxWx). Within Mendelian concept (not considering recombination), a test cross yielding all four possible phenotypes at a even proportion requires an exhaustive allelic pool from the non-recessive parent. Among b) and e), only genotype DdWw from b) is capable of fulfilling this requirement, as it gives four different gametes with alleles DW, Dw, dW, and dw.