Question

If Aabb crossed with aaBb, then the genotypic ratio of its progeny will be
(a) 9 : 3 : 3: 1
(b) 1: 2: 1
(c) 1: 1: 1: 1
(d) 4: 4

Answer 1

Hint: This type of cross between two heterozygous parents results in the production of progeny having four different genotypes. That will represent the genotypic ratio of the above cross.

Complete answer:
If Aabb is crossed with aaBb then the genotypic ratio of its progeny will be 1: 1: 1: 1. When Aabb and aaBb are crossed together the gametes formed are Ab, ab, and aB, ab. The offspring produced by these gametes are AaBb, Aabb, aaBb, and aabb. In all these four offsprings there are no similarities found in their genotype. So, their genotypic ratio will be 1: 1: 1: 1.

Additional Information:
-When genes for certain traits are crossed, the number of times a characteristic of an organism will appear in the offspring shows the genotypic ratio.
-Using the Punnett square grid all the phenotypic variations for the offspring predicted when the male and female gametes are crossed together.
-To determine the genotypic ratio we will count the number of times each combination of genes appears in the grid starting from the upper left square.
-9 : 3 : 3: 1 is a typical phenotypic ratio of Mendelian dihybrid cross in which the alleles of two different genes assort independently into gametes.
-1: 2: 1 is a typical genotypic ratio of Mendelian monohybrid cross. Here each factor in a pair gets separated during gamete formation so that every gamete will have one factor for each character.
-4: 4 can be written as 1: 1 which represents a cross between a heterozygote and a homozygous parent. Here only one gene is involved in the phenotype.

So, the correct answer is, ‘1: 1: 1: 1’.

Note:
-In genetics, the ratio describes the number of times a genotype appears in the offspring after a test cross. This ratio will be called the genotypic ratio.
-1: 1: 1: 1 is also a phenotypic ratio of a typical Mendelian test cross. In this type of cross, the alleles of two genes assort independently into gametes.
-The test cross is done to find out the genotype of parents and is only possible to determine if we know the genotype of offspring.