Question

How many types and in what ratio the gametes are produced by a dihybrid heterozygous?
(A)4 types in the ratio of 9:3:3:1
(B)2 types in the ratio of 3:1
(C)3 types in the ratio of 1:2:1
(D)4 types in the ratio of 1:1:1:1

Answer 1

Hint: A Dihybrid cross is a cross between two different genes that differ in two observed traits. According to Mendel's declaration, between the alleles of both these loci, there is an alliance of completely dominant - recessive traits.

Complete answer:
Option (A)4 types in the ratio of 9:3:3:1
This 9:3:3:1 phenotypic ratio is the classic Mendelian ratio for a dihybrid cross in which the alleles of two different genes assort independently into gametes. This option is not correct.
Option (B)2 types in the ratio of 3:1
This option is not correct.
Option (C)3 types in the ratio of 1:2:1
This option is not correct.
Option (D)4 types in the ratio of 1:1:1:1
The cross between two homozygous parents considering two pairs of contrasting alleles is called a dihybrid cross e.g., YYRR (yellow and round ) is crossed with your (green and wrinkled). The gametes formed are YR and yr. After fertilization, the F1 heterozygote will be formed i.e YyRr (yellow and round). On selfing F1 we get two possible combinations i.e YR, Yr, yR, yr. Therefore four types of gametes are formed in the ratio of 1:1:1:1.

Hence the correct answer is OPTION(D)

Note: A hybrid organism is one that is heterozygous, which means that it carries two different alleles at a particular genetic position or locus. Hence, a dihybrid organism is one that is heterozygous at two several genetic loci. Organisms in this primary cross are called the parental, or P generation.