Question

A cross between F1 hybrid and recessive parent gives a ratio of ______
A) 3:1
B) 1:1
C) 2:1
D) 4:1

Answer 1

In Mendelian genetics, there are several different kinds of crosses that are used to select genes that assort independently. When the cross is between an F1 hybrid with the homozygous recessive parent, it is known as a Test Cross.

Complete answer:
Let’s take an example of Tt x tt. When these two individuals are crossed, there will be two progeny who have the genotype Tt and two who have the genotype tt. The genotypic ratio will therefore be 1:1. And similarly, the phenotype ratio of will be 1:1 of tall to dwarf plants. Option B is the correct answer.
A phenotype ratio of 3:1 can be found when heterozygous individuals are crossed. T x Tt, will give offspring that are TT, Tt, tT, tt. Phenotypically, it would be 3:1 for tall to dwarf plants. Option A is incorrect.
When two heterozygotes are crossed, a genotype ratio of 1:2:1 is seen. However, sometimes one allele can be lethal, and a phenotype ratio of 2:1 results. Answer C is incorrect
In this type of cross, there is no way a 4:1 ratio is expected. Option D is incorrect.
In genetics, phenotypes are the visible characteristics that are seen. A genotype is the gene combination present. The same phenotype may be observed even with different genotypes. For example, when crossing dominant and recessive alleles for homozygous parents in a typical monohybrid cross, F1 generation would be genotypic ally 1:2:1, but phenotypically 3:1.

Hence the correct answer is option ‘B’.

Note: Genetic inheritance of characters will differ greatly depending on whether the genes assort independently of each other, or they are linked In this case, Punnett squares would not give an accurate answer.