Question

A breeder crossed a pure breed tall pea plant having white flowers to a pure bred short pea plant with blue flowers. He obtained 202 F${}_1$ progeny and found that they are tall having white flowers. Upon selfing these plants he obtained a progeny of 2160 plants Approximately, how many of these are likely to be short and blue flowers?

• A. 1215
• B. 405
• C. 540
• D. 135

Answer 1

The correct option is D 135

We know that a pure breeding homozygous dihybrid cross will give Heterozygous dihybrid F1 progeny. So by this observation, we find that Tallness and White flowers are a dominant trait in the parent plant. So on selfing in an F1 generation the cross will be similar to Heterozygous dihybrid cross i.e., TtWw x TtWw (where T is dominant allele over t for a gene of height while W is dominant over w allele for the color of flower)

The typical phenotypic ratio of this cross is expected to be

9:3:3:1:: Tall and white flower: Tall and blue flower: Short and white flower: Short and blue flower.

So, here we find that out of 16 progeny 1 progeny will have short and blue flowers

So, in 2160 progeny plants, number of plants with the double recessive trait will be = 1/16 x 2160

= 135

So, the correct answer is '135'.