Question

State and explain Mendel's Law of Independent Assortment using a dihybrid cross.

Hint:

A {dihybrid cross} involving two traits produces a characteristic {9:3:3:1 phenotypic ratio}, demonstrating Mendel's Law of Independent Assortment.

Answer 1

Concept: Gregor Mendel proposed several laws of inheritance based on his experiments with pea plants. One of these is the Law of Independent Assortment, which explains how different traits are inherited independently of each other.
Step 1:Statement of the Law The Law of Independent Assortment states that the alleles of two different genes segregate independently during the formation of gametes. Therefore, the inheritance of one trait does not affect the inheritance of another trait.
Step 2:Dihybrid Cross Example Consider a cross between pea plants differing in two traits:

• Seed shape: Round (R) is dominant over wrinkled (r).
• Seed color: Yellow (Y) is dominant over green (y).

Parental Generation (P): \[ RRYY \; (\text{Round, Yellow) \times rryy \; (\text{Wrinkled, Green) \] Gametes: \[ RY \quad \text{and \quad ry \] First Filial Generation (F\(_1\)): \[ RrYy \] All offspring show the dominant traits (Round and Yellow).
Step 3:Second Filial Generation (F\(_2\)) When the F\(_1\) plants \((RrYy)\) are crossed with each other: \[ RrYy \times RrYy \] The gametes produced are: \[ RY, \; Ry, \; rY, \; ry \] The phenotypic ratio obtained in the F\(_2\) generation is: \[ 9 : 3 : 3 : 1 \]

• 9 Round Yellow
• 3 Round Green
• 3 Wrinkled Yellow
• 1 Wrinkled Green

This ratio shows that the two traits assort independently.