Question

When a dihybrid cross is fit into a Punnett square with 16 boxes, the maximum number of different phenotypes available are-
A. 8
B. 4
C. 12
D. 16

Answer 1

As Mendel defined, a dihybrid cross is a cross between two organisms that have two different genes/ lines and have two different observable or phenotypic traits. Phenotype is the physical expression of a gene.

Complete answer:
The mating experiment between two organisms, who have two different alleles at a particular locus for an identical trait, is called the Dihybrid cross. These two organisms will have two phenotypic expressions for this gene. One of the expressions will be dominant, while the other will be recessive. Dominant traits are those traits that are shown in the homozygous as well as the heterozygous state. Recessive traits are only seen in the homozygous stage. They get dominated by the dominating allele in the heterozygous condition.
Let us answer this question through an example.

Fig: The Punnett square shown above depicts a dihybrid cross between seeds.

The above Punnett square is a cross between seeds that have different expressions for the traits- seed shape and seed color. Seed shape is shown by the dominant, round shape (R) and recessive, wrinkled shape(r). Seed color is shown by the dominant, yellow color (Y) and recessive, white color (y). The F1 cross will form 4 types of gametes- RY(round and yellow), Ry(round and white), rY(wrinkled and yellow), and ry(wrinkled and white). The F2 cross among these 4 gametes will form a total of 16 combinations of gametes. Both traits will pass on to the next generation, or gametes independently of one another. The phenotypic ratio will be 9:3:3:1, and the genotypic ratio will be 1:2:1:2:4:2:1:2:1.

There will be 9 different genotypic combinations and 4 different phenotypes. These four phenotypes will be- round and yellow, round and white, white and wrinkled, wrinkled and yellow.
Option B: Four different types of phenotypes are found. Therefore, this is the correct option.
All the other options are irrelevant.

Hence, the correct answer is option (B)

Note: Gregor Mendel was the first scientist to perform the dihybrid cross on the seeds of the pea plant. He deduced the Law of Independent assortment from this cross by studying the relationship between the different allelic pairs.