Question

Identify the correct sequence of steps in a dihybrid cross to test Mendel's Law of Independent Assortment
A. Selection of two traits in the parent generation.
B. Crossing of pure - breeding parents.
C. Analysis of phenotypic ratios in the F₂ generation.
D. Observations of gamete combinations in the F₁ generation.
Choose the correct answer from the options given below:

• A. A, B, C, D
• B. A, B, D, C
• C. B, A, D, C
• D. B, C, A, D

Hint:

Remember the flow of any Mendelian experiment: \textbf{P} (Parents) \(\rightarrow\) \textbf{F₁} (First Filial) \(\rightarrow\) \textbf{F₂} (Second Filial). You must set up the parents first (A, B), then produce and analyze the F₁ (D), and finally produce and analyze the F₂ (C).

Answer 1

The Correct Option is B

Step 1: Concept Overview:
The question focuses on the correct experimental procedure for a Mendelian dihybrid cross. This cross investigates the simultaneous inheritance of two traits, demonstrating the Law of Independent Assortment.
Step 2: Detailed Explanation:
Here's a breakdown of the experimental steps:

A. Trait Selection: Begin by selecting two distinct, contrasting traits to study in the parent generation (e.g., pea seed shape and color).
B. Pure-Breeding Cross: Perform a parental (P generation) cross using pure-breeding (homozygous) parents. One parent should be dominant for both traits, the other recessive (e.g., RRYY x rryy).
D. F₁ Gamete Observation: The offspring of the P cross constitute the F₁ generation, all heterozygous for both traits (e.g., RrYy). Self-cross these F₁ individuals. Independent assortment is demonstrated by the F₁ generation producing four gamete types (RY, Ry, rY, ry) in equal proportions. Step D involves generating and understanding these F₁ gametes, which create the F₂ generation.
C. F₂ Phenotypic Ratio Analysis: The self-cross of the F₁ generation yields the F₂ generation. Count the offspring and analyze their phenotypic ratios. Independent assortment predicts an approximate 9:3:3:1 ratio. This analysis serves as the ultimate test of the law.
Step 3: Solution:
The correct experimental order is: Trait Selection (A) \(\rightarrow\) Pure-Breeding Cross (B) \(\rightarrow\) F₁ Observation for next cross (D) \(\rightarrow\) F₂ Analysis (C), corresponding to A, B, D, C.