Question

In a dihybrid cross F2 generation offspring show four different phenotypes, while the genotypes are of ______types.
A. Six
B. Nine
C. Eight
D. Sixteen

Answer 1

Hint: Genotype is the genetic makeup of the individual. Genotype depends on the genes which are inherited from parents .Phenotype is an expression of characters. The genotype determines individual characteristics (such as height, skin color, hair color, etc.), which are expressed slowly during development. These individual characteristics also depend on their environment.

Complete answer:
Mendel dihybrid cross

Gametes	RY	rY	Ry	ry
RY	RRYYRound, yellow	RrYYRound, yellow	RRYyRound, yellow	RrYyRound, yellow
rY	RrYYRound, yellow	rrYYwrinkled, green	RrYyRound, yellow	rrYyWrinkled, yellow
Ry	RRYyRound, yellow	RrYyRound, yellow	RRyyRound,green	RryyRound, green
ry	RrYyRound, yellow	rrYyWrinkled, yellow	RryyRound, green	rryyWrinkled, green

So from the above table it’s clear that
Genotypic ratio $:1:2:2:4:1:2:1:2:1$



Hence 9 different genotypes are possible in Mendel dihybrid cross and the correct option is (B).
Phenotypic ratio of dihybrid cross is $9:3:3:1$

Note: Law of segregation: This law states that alleles are separated from each other during gamete formation and transmitted to different gametes in the same number. In other words, when the alleles for two contrasting marks are combined into a hybrid, they do not mix, contaminate, or influence each other while together.
Law of dominance: The law of domination states that when two alternative forms of a trait or character (gene) are present in an organism, only one factor is expressed in F1 offspring and is called dominant, while the other factor which remains closed is called recessive.
Law of independent assortment: This was the second law of inheritance Mendel discovered. This law states that when two pairs of genes enter an F1 combination, they have independent dominant effects. These genes divide when gametes are formed, but the areas occur randomly and are quite independent.
The amount of gene activity and the influence of the environment on it leads to the formation of visible traits called phenotypes.