Norway rats have 42 chromosomes in their diploid cells. If such a cell enters meiosis, how many chromosomes and double-helical molecules of DNA will be present in each daughter cell at the end of meiosis II?
a. 21 chromosomes and 21 double-helical DNA molecules
b. 21 chromosomes and 42 double-helical DNA molecules
c. 42 chromosomes and 42 double-helical DNA molecules
d. 42 chromosomes and 84 double-helical DNA molecules

Verified step by step guidance

1. Step 1: Understand the concept of diploid and haploid cells. Diploid cells contain two sets of chromosomes (one from each parent), while haploid cells contain only one set of chromosomes. Meiosis reduces the chromosome number from diploid (2n) to haploid (n).
2. Step 2: Recall the chromosome number in Norway rats. The diploid number is 42 chromosomes (2n = 42). During meiosis, this number is halved, resulting in haploid cells with 21 chromosomes (n = 21).
3. Step 3: Consider the process of meiosis. Meiosis consists of two divisions: meiosis I and meiosis II. At the end of meiosis I, homologous chromosomes are separated, but each chromosome still consists of two sister chromatids. At the end of meiosis II, sister chromatids are separated, resulting in daughter cells with single chromatids.
4. Step 4: Determine the number of double-helical DNA molecules. At the end of meiosis II, each chromosome consists of a single chromatid, which corresponds to one double-helical DNA molecule. Since there are 21 chromosomes in each haploid daughter cell, there will also be 21 double-helical DNA molecules.
5. Step 5: Match the findings to the answer choices. Based on the analysis, the correct answer is: 21 chromosomes and 21 double-helical DNA molecules.

Key Concepts

Meiosis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four genetically diverse daughter cells. It consists of two sequential divisions: meiosis I and meiosis II. During meiosis I, homologous chromosomes are separated, while meiosis II resembles mitosis, where sister chromatids are separated. This process is crucial for sexual reproduction, producing gametes with half the diploid number of chromosomes.

Chromosome Number

In diploid organisms, chromosomes exist in pairs, with one set inherited from each parent. Norway rats have 42 chromosomes in their diploid cells, meaning they have 21 pairs. During meiosis, the diploid number is halved, resulting in haploid gametes that contain only one chromosome from each pair. Thus, after meiosis, each daughter cell will have 21 chromosomes.

Double-Helical DNA Molecules

Each chromosome consists of a single double-helical DNA molecule. During the S phase of the cell cycle, before meiosis begins, each chromosome is replicated, resulting in two sister chromatids per chromosome. However, during meiosis II, the sister chromatids are separated, leading to each daughter cell containing one double-helical DNA molecule per chromosome. Therefore, at the end of meiosis II, each daughter cell will have 21 double-helical DNA molecules.