Question

In a dihybrid cross between RRYY and rryy parents the number of RrYy genotypes possible in f2 generation will be
A) 4
B) 3
C) 2
D) 1

Answer 1

Hint: Dihybrid cross was first demonstrated by Mendel on a pea plant. In this type of cross, the mating is done between two organisms involving two traits. The hybrid organism obtained is heterozygous and carries two different alleles at the same locus.

Complete answer:
A dihybrid cross helps us in understanding the inheritance of two different traits in an organism at the same time. According to Mendel, in a cross, one character is dominant which is expressed and the other is recessive which is not expressed.

The parent organism possesses different pairs of alleles for each trait. One of the parents has a homozygous dominant allele and the other has homozygous recessive alleles. Two laws, Law of Segregation and the law of independent assortment, were given as a result of dihybrid cross. The dihybrid cross helped in establishing relationships between different allelic pairs.

According to the question, the cross is made between RRYY and rryy.
F1 generation- RRYY X rryy
The gametes are RY and ry.
The cross results in RrYy
F2 generation- Self cross is done between RrYy.
The gametes formed are RY, Ry, rY, ry
The offsprings produced is represented as:

	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	rrYY	rrYy
ry	RrYy	Rryy	rrYy	rryy

The number of RrYy heterozygous hybrids obtained are 4.
The number of homozygous hybrids RRYY, rryy are 1,1
The number of RRYy-2
The number of RrYY-2
The number of RRyy-1
The number of Rryy-1
The number of rrYY-1
The number of rrYy-2

Thus, the correct answer is option ‘A’.

Note: The phenotype refers to the observable traits of an individual. The genotype refers to the collection of genes. The phenotypic ratio of the dihybrid cross is 9:3:3:1. The phenotypic ratio of the monohybrid cross is 3:1 and the genotypic ratio is 1:2:1. This ratio holds good when one allele is dominant and the other is recessive.