Question

What will be the genotypic ratio of the cross between Rr and rr?
A. 1:2:1
B. 3:1
C. 1:1
D. 1:1:1

Answer 1

Genotype shows the genes involved in the expression of a particular phenotype. Genotypic ratio tells how many times a particular genotype or character appeared in the offspring after a cross.

Complete answer:
Genotype is the genetic constitution that helps in the expression of a particular character which is visible by the phenotype or physical appearance. We make a Punnett square to study the genotype and phenotype after a cross. In this question we have one homozygous allele rr with recessive character r and Rr is a heterozygous allele with dominant character R, the cross will be:

| R| r
---|---|---
r| Rr| rr
r| Rr| rr

In this cross 2 individuals have similar genotypes so the genotypic ratio will be 1:1.
Hence, the correct answer is option (C).

Additional information:
Gregor John Mendel is the father of Genetic, he discovered all the crosses and was the first person to use mathematics to explain biological phenomena.
He studied garden peas – Pisum sativum and observed around 7 major characteristics and the pattern of their transfer into the next generation.
These crosses with heterozygous alleles help to know about the dominant and recessive traits. Dominant alleles suppress the expression of recessive alleles.
Recessive alleles need a homozygous (rr) condition for their expression where both the alleles are similar, Dominant alleles can be expressed in homozygous (RR) as well as heterozygous conditions (Rr)
Test cross is done sometimes when the genotype of one parent is known but the genotype of the other parent is unknown.

Note: Mendel stated a law of dominance which explains about the expression of dominant traits and their chances to be transferred into the next generation which are maximum. He said that when recessive and dominant alleles are present together then only the dominant alleles get transferred into the offspring and they express themselves genotypically and phenotypically.