Question

The number of $F_2$ plants found similar to $F_1$ phenotype and genotypes respectively in a total of 128 plants in $F_2$ progeny of a mendelian dihybrid cross are

• A. 48, 32
• B. 72, 32
• C. 48, 24
• D. 72, 48

Answer 1

The correct option is B 72, 32

A dihybrid cross between two pure varieties that differ in two pairs of contrasting characters obtains $F_1$ generation. Selfing between two hybrids give the phenotypic ratio of 9:3:3:1 in $F_2$ generation, out of which 9/16 have the phenotype identical to $F_1$ hybrid. Therefore, out of 128 plants in $F_2$ generation, a number of the plant which are phenotypically identical to $F_1$ hybrid would be 9/16 * 128= 72. The genotypic ratio for $F_2$ generation is 1: 2 :1 : 4 : 2 : 2 :1 : 2 :1ttrr out of which 4/16 have the genotype identical to $F_1$ hybrid. Therefore, out of 128 plants in $F_2$ generation, a number of the plant which are genotypically identical to $F_1$ hybrid would be 4/16 * 128= 32. This makes option B correct answer.