Question

What is the total number of genotypes and phenotypes in a dihybrid test cross ?

(A).

9

(B).

8

(C).

16

(D).

13

Answer 1

The correct option is C

Explanation of the correct answer:

1. ​The cross between F1 heterozygous parent and homozygous parent for two characters is called dihybrid test cross.
2. We can assume that the genotype of one parent is RrYy, if R is the gene for seed shape and Y is the gene for seed colour.
3. Then the genotype of the other parent involved in the dihybrid test cross will be rryy, i.e., recessive for all traits.
4. Then the test cross can be represented as follows:
5. 
6. Therefore, total number of genotypes and phenotypes are 4 + 4 = 8.

Explanation of the incorrect answers:

Option A:

1. ​The number of genotypes in dihybrid test cross are 4.
2. The number of phenotypes in dihybrid test cross are also 4.
3. Therefore, total number of genotypes and phenotypes are 4 + 4 = 8.

Option B:

1. ​The number of genotypes in dihybrid test cross are 4.
2. The number of phenotypes in dihybrid test cross are also 4.
3. Therefore, total number of genotypes and phenotypes are 4 + 4 = 8.

Option D:

1. ​The number of genotypes in dihybrid test cross are 4.
2. The number of phenotypes in dihybrid test cross are also 4.
3. Therefore, total number of genotypes and phenotypes are 4 + 4 = 8.

Final answer: The total number of genotypes and phenotypes in a dihybrid test cross are 8.