Consider a diploid organism with 2n = 6. This cell is in metaphase I of meiosis. How many chromosomes are aligned at the metaphase plate?

• A. 3
• B. 1
• C. 6
• D. 12

Answer: (A)

Verified step by step guidance

1. Understand that the organism is diploid with 2n = 6, meaning it has 6 chromosomes total in its somatic cells.
2. Recall that during metaphase I of meiosis, homologous chromosomes pair up as bivalents (tetrads) and align at the metaphase plate.
3. Since the organism is diploid with 2n = 6, it has n = 3 pairs of homologous chromosomes.
4. At metaphase I, these 3 pairs (bivalents) align at the metaphase plate, not individual chromatids or single chromosomes.
5. Therefore, the number of chromosomes aligned at the metaphase plate corresponds to the number of homologous pairs, which is 3.