Question

A homozygous pea plant bearing yellow (Y) and round seeds (R) is crossed with a homozygous plant bearing green (y) and wrinkled seed (r ) :-

1. Give the genotype and phenotype of the plants of the F₁ generation.
2. Mention the possible combinations of the gametes that can be obtained from the F₁ hybrid plant.
3. State Mendel's law of independent assortment.
4. Mention the phenotypes of the offspring obtained in the F₂ generation.
5. What is the phenotypic ratio obtained in F₂ generation?

Answer 1

Dihybrid Cross:

1. In the question, a pea plant is homozygous for the traits i.e., seed color and seed shape.
2. One plant is homozygous dominant with yellow and round seeds (with uppercase letters Y and R) and the other is homozygous recessive with green and wrinkled seeds (with lowercase letters y and r).
3. It is a dihybrid cross as two traits are involved in the cross.

i. Genotype and phenotype of the plants of the F₁ generation

1. Genotype is the genetic makeup of the organism.
2. Phenotype is the physical appearance of the organism.
3. If a dihybrid cross is done between two given plants then the F₁ generation offspring would have the following genotype and phenotype
   1. Genotype: RrYy
   2. Phenotype: Round yellow

ii. Possible combinations of the gametes that can be obtained from the F₁ hybrid plant

1. According to the law of independent assortment which states that "during a dihybrid cross (crossing of two pairs of traits), an assortment of each pair of traits is independent of the other”. The two factors of a character separate independently of the other pair.
2. The gene Y may combine with the dominant gene R or the recessive gene r and gene y can combine with the dominant or recessive gene to form a gamete.
3. Types of gametes produced are YR, Yr, yR, and yr.

iii. Mendel's law of independent assortment

1. The Law of independent assortment states that when two pairs of contrasting characters are combined in a hybrid, the segregation of members of one pair of a gamete is independent of members of another pair of gametes.
2. It is one of the laws of inheritance given by Mendel.

iv. Phenotypes of the offspring obtained in the F₂ generation

1. The table below shows a dihybrid cross between individuals of the F₁ generation. The phenotypes obtained in the F₂ generation are
   1. 9 round and yellow seeds
   2. 3 round and green seeds
   3. 3 wrinkled and green seeds
   4. 1 wrinkled and green seed.

v. Phenotypic ratio obtained in the F₂ generation?

1. With the help of the Punnett square in the picture, the ratio obtained in the F₂ generation can be given as 9:3:3:1.