Genotypic Ratio of a Dihybrid Cross (NEET Biology)

Genotypic ratio of a dihybrid cross is

A. 12:3:1

B. 15:1

C. 1:2:1

D. 1:2:2:4:1:2:1:2:1

Hint: Genotype refers to the genetic makeup of an organism’s DNA that determines a specific trait. Phenotype, on the other hand, refers to the observable characteristics or traits that result from the gene expression. For instance, when a red flower (RR) is crossed with a white flower (rr), the resulting gametes will be (Tt). Therefore, (Tt) represents the genotype for that trait, while the phenotype is “tall.”

Complete answer:

A dihybrid cross involves studying two traits, such as the shape and color of a pea plant. Mendel used this method to illustrate the law of independent assortment. 

Let’s explore the dihybrid cross along with the genotypic and phenotypic ratios using an example: In this case, the two traits are the yellow and green color of the pod, and the round and wrinkled shape of the seed in the pea plant. 

The dominant characteristics are yellow color and round shape. The dominant alleles are represented as yellow – YY and round – RR. 

On the other hand, the recessive traits are green color and wrinkled shape. These can be represented by green – yy and wrinkled – rr.

To better comprehend the independent segregation of the two gene pairs, we can use a Punnett square.

Now let us try to find out the ratio:

Phenotypic ratio –

That is, 

9:3:3:1

Genotypic ratio –

That is, 

1:2:2:4:1:2:1:2:1

Therefore the correct option is D.

Note: G. Mendel is known as the father of genetics. IIn the 19th century, he carried out studies on pea plants. Initially, he performed a monohybrid cross, and from these experiments, he formulated the foundational principles of inheritance. The first principle is the law of dominance, while the second is the law of segregation. When Mendel crossed plants with two traits, he established the law of independent assortment.