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. Understand that diploid cells (2n) have two sets of chromosomes. For Norway rats, the diploid number is 42, meaning there are 21 pairs of chromosomes.
2. Recognize that meiosis is a type of cell division that reduces the chromosome number by half, resulting in four haploid (n) cells. Each haploid cell will have half the number of chromosomes as the original diploid cell.
3. At the end of meiosis I, the cells are haploid, but each chromosome still consists of two sister chromatids. Thus, each cell has 21 chromosomes, each made of two chromatids, so there are 42 double-helical DNA molecules.
4. During meiosis II, the sister chromatids separate, and the cells divide again, but the number of chromosomes does not change. Each of the four resulting daughter cells ends up with 21 chromosomes.
5. Since the chromatids have separated, each chromosome now consists of a single double-helical DNA molecule. Therefore, each daughter cell has 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 essential for sexual reproduction, producing gametes with half the original chromosome number.

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, the number of double-helical DNA molecules is equal to the number of chromosomes at the end of meiosis II, as the sister chromatids are separated but not replicated again. Therefore, each daughter cell will have 21 double-helical DNA molecules.