Which of these gametes contains one or more recombinant chromosomes

Which of these gametes contains one or more recombinant chromosomes?

Gamete arrangement after meiosis with a crossing over. A cell contains one large blue chromosome, one large red chromosome, one small blue chromosome, and one small red chromosome. This cell can form 8 types of gametes, 5 of them are labeled A through E. Gamete A contains 1 long blue and 1 short blue chromosomes. Gamete B contains 1 long blue and 1 short blue chromosomes; both have red ends. Gamete C contains 1 long red and 1 short red chromosomes; both have blue ends. Gamete D contains 1 long red and 1 short red chromosomes. Gamete E contains 1 long red and 1 short blue chromosomes.

A and B
B and C
D and E
A and D
A and C

The correct answer and explanation is :

The correct answer is A and B.

Here’s why:

During meiosis, homologous chromosomes exchange genetic material during a process called crossing over. This results in the formation of recombinant chromosomes, which carry new combinations of alleles that were not present in the original chromosomes. These recombinant chromosomes then segregate into different gametes, resulting in genetic diversity.

In the scenario described, we have four chromosomes: two large (one blue and one red) and two small (one blue and one red). The following types of gametes are listed:

1. Gamete A: Contains 1 long blue and 1 short blue chromosome.
2. Gamete B: Contains 1 long blue and 1 short blue chromosome; both have red ends.
3. Gamete C: Contains 1 long red and 1 short red chromosome; both have blue ends.
4. Gamete D: Contains 1 long red and 1 short red chromosome.
5. Gamete E: Contains 1 long red and 1 short blue chromosome.

Now, let’s break down what happens during crossing over:

• Recombinant chromosomes are those that have undergone crossing over. This results in a chromosome that has a mixture of the alleles from both homologous chromosomes, i.e., a portion of the blue chromosome might swap with a portion of the red chromosome.
• Non-recombinant chromosomes remain unchanged because no crossing over occurred between the two homologous chromosomes, meaning the chromosomes are inherited in their original form.

Analyzing the gametes:

• Gamete A (1 long blue, 1 short blue): This gamete is non-recombinant because both chromosomes are blue and did not undergo crossing over.
• Gamete B (1 long blue, 1 short blue, both with red ends): This gamete is recombinant. The crossing over between the blue and red chromosomes has resulted in blue chromosomes with red portions, making it a recombinant chromosome.
• Gamete C (1 long red, 1 short red, both with blue ends): This gamete is recombinant. The crossing over between the red and blue chromosomes has resulted in red chromosomes with blue portions, making it a recombinant chromosome.
• Gamete D (1 long red, 1 short red): This gamete is non-recombinant because it contains the original red chromosomes without any mixing of blue portions.
• Gamete E (1 long red, 1 short blue): This gamete is non-recombinant because it contains a red chromosome and a blue chromosome that were inherited without undergoing any crossover.

Conclusion:

Gametes A and B contain recombinant chromosomes. Gamete A is non-recombinant, but gamete B contains recombinant chromosomes as a result of crossing over. Therefore, the correct answer is A and B.