To obtain recombinant products during meiosis, a double-strand break in the DNA yields crossovers needed for chiasmata formation. The progression of the non-crossover and crossover pathways begins with the formation of D loop, however, it may not result in the production of recombinant gametes.

Following statements are made regarding recombination:

A. Expansion of D-loop takes place in non-crossover pathway, but not in the crossover pathway.
B. Expansion of D-loop takes place in crossover pathway, but not in the non-crossover pathway.
C. Ejection of elongating strand takes place in the non-crossover pathway, but not in the crossover pathway.
D. Ejection of elongating strand takes place in the crossover pathway, but not in the non-crossover pathway.

Which one of the following options represents the correct combination of statements that explain the formation of recombinant gametes?

Correct option is B

Correct Answer: (2) B and C

Explanation:

Let's break down the statements and their relevance to recombination during meiosis:

A. Expansion of D-loop takes place in non-crossover pathway, but not in the crossover pathway.

• Incorrect: The D-loop formation is crucial in both the crossover and non-crossover pathways. Both pathways involve the formation of the D-loop as a critical intermediate step. Therefore, this statement is incorrect.

B. Expansion of D-loop takes place in crossover pathway, but not in the non-crossover pathway.

• Correct: The D-loop expansion is specifically involved in the crossover pathway. The expansion and stabilization of the D-loop is essential for crossovers, where the strands of homologous chromosomes exchange genetic material. This statement is correct.

C. Ejection of elongating strand takes place in the non-crossover pathway, but not in the crossover pathway.

• Correct: In the non-crossover pathway, the elongating strand that is involved in the exchange is ejected without further recombination, meaning there is no crossover event. In this pathway, the exchanged DNA doesn't result in a crossover product, making this statement accurate.

D. Ejection of elongating strand takes place in the crossover pathway, but not in the non-crossover pathway.

• Incorrect: This statement is incorrect because the ejection of the elongating strand actually occurs in the non-crossover pathway. In the crossover pathway, the elongating strand is incorporated into the crossover event, leading to recombination.

Information Booster:

• Crossover pathway involves the exchange of genetic material between homologous chromosomes, leading to the production of recombinant gametes.

• Non-crossover pathway results in the gene conversion without exchange of entire chromosomal arms, leading to non-recombinant gametes.