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: Understanding the Concept:
The question asks for the correct experimental procedure for a Mendelian dihybrid cross, which is designed to study the inheritance of two different traits simultaneously and demonstrate the Law of Independent Assortment.
Step 2: Detailed Explanation:
Let's outline the logical steps of the experiment:

A. Selection of two traits in the parent generation: The experiment begins with the scientist choosing two distinct, contrasting traits to study (e.g., seed shape and seed color in peas).
B. Crossing of pure - breeding parents: The next step is to perform the parental (P generation) cross. This involves crossing two parents that are pure-breeding (homozygous) for the selected traits, one dominant for both and the other recessive for both (e.g., RRYY x rryy).
D. Observations of gamete combinations in the F₁ generation: The offspring of the P cross are the F₁ generation. They are all heterozygous for both traits (e.g., RrYy). Mendel then self-crossed these F₁ individuals. The key to independent assortment is observing that the F₁ generation produces four different types of gametes (RY, Ry, rY, ry) in equal proportions. Step D, "Observations of gamete combinations in the F₁ generation," refers to this step of generating and understanding the gametes from the F₁ that will create the F₂ generation.
C. Analysis of phenotypic ratios in the F₂ generation: The offspring of the F₁ self-cross are the F₂ generation. The final step is to count the offspring and analyze their phenotypic ratios. If the genes assort independently, this ratio will be approximately 9:3:3:1. This analysis is the ultimate test of the law.
Step 3: Final Answer:
The correct experimental sequence is: Select traits (A) \(\rightarrow\) Cross pure parents (B) \(\rightarrow\) Observe F₁ and its gametes for the next cross (D) \(\rightarrow\) Analyze F₂ results (C). This corresponds to the order A, B, D, C.