Question

Ratio 1: 1: 1: 1 is obtained from a cross of _________.
A. RRYY x rryy
B. RRYy x rrYy
C. RrYY x Rryy
D. RrYy x rryy

Answer 1

Gregor Johann Mendel introduced the test cross for the first time in the genetics. This test involves the crossing of an unknown individual with a phenotypically recessive parent. This test will help in determining the zygosity of another unknown individual which was crossed.

Complete answer:
In a dihybrid test cross, dihybrid individuals are crossed with a homozygous recessive parent. The phenotypic proportions of the offsprings produced could be analyzed for getting the results. The unknown individual may be heterozygous or homozygous. The presence of one dominant allele and the other recessive allele indicates heterozygosity while the individual is homozygous if either both the alleles are dominant or both the alleles are recessive.
The phenotypic ratio of the Mendelian test cross involving the assortment of the two genes independently is 1:1:1:1.
In the given case, the crossing of RrYy (dihybrid) with rryy (homozygous recessive parent) gives 1:1:1:1 phenotypic ratio and 1:1:1:1 genotypic ratio.

Parents	RrYy	x	rryy
Gametes	RY, rY, yR, yr	x	ry

RrYy	rrYy	Rryy	rryy
1	1	1	1

So, the correct answer is option “D” that is Ratio 1: 1: 1: 1 is obtained from a cross of RrYy x rryy.

Note:
These test crosses could be utilized to determine the genetic makeup of the dominant parent. Further, by using a test cross the genotypes of various organisms could be explored. Earlier this test cross was employed to determine the types of alleles that are existing in a particular genotype of an individual.