Question

A tall violet flowered plant (TTVV) is crossed with a dwarf white flowered plant (ttvv). When the $F_1$ plants are self-pollinated, a total of 1600 $F_2$ plants are produced. How many plants of $F_2$ generation are similar to the original parents in terms of both genotype and phenotype?

• A. 900
• B. 300
• C. 100
• D. 200

Answer 1

The correct option is D

200

This is a typical dihybrid cross. Both original parents are homozygous, so two different types of gametes will be formed- (TV) and (tv) respectively. The $F_1$ progenies will be heterozygous with the genotype TtVv. Four different gametes are formed by the $F_1$ plants- (TV), (Tv), (tV), (tv). The genotype of the $F_2$ progenies are worked out using the Punnett square below


As shown here genotype ratio of the $F_2$ generation is 1:1:2:2:4:2:2:1:1.
And 1 homozygous dominant (TTVV) and 1 homozygous recessive (ttvv) progenies are produced, which are the genotypes of the original parent plants. Therefore $\frac{1}{16}$th of the 1600 $F_2$ progenies are homozygous dominant (TTVV), that is $\frac{1}{16}\times 1600=100$ and $\frac{1}{16}\times 1600=100$ are homozygous recessive (ttvv). 100 + 100 = 200. Thus a total of 200 $F_2$ progenies have the genotype of the original parents.