In an organism with 2n=20 (n=10) chromosomes, how many:
Chromosomes in telophase II
Chromosomes in G2
Chromatids metaphase I
Chromatids prophase I
DNAs anaphase
DNAs prophase II
To answer these questions, we need to understand the stages of meiosis and the concepts of chromosomes, chromatids, and DNA replication. Meiosis is the process by which cells divide to produce gametes (sperm and eggs) with half the number of chromosomes as the parent cell. It consists of two rounds of division, known as meiosis I and meiosis II.
In an organism with 2n=20 chromosomes (where n is the haploid number), the total number of chromosomes in each cell is 20. Let's break down each question and explain how to determine the answers:
1. Chromosomes in telophase II:
During telophase II, the chromosomes are at their most condensed state and are starting to decondense. Meiosis II follows quickly after meiosis I, and there is no DNA replication between these two phases. Therefore, the number of chromosomes in telophase II will be the same as the number of chromosomes in meiosis I, which is 20.
2. Chromosomes in G2:
G2 (Gap 2) is the second stage of interphase in the cell cycle, which occurs between the S phase (DNA synthesis) and mitosis/meiosis. During G2, the cell prepares for division by synthesizing proteins and other structures. The chromosome number in G2 remains the same as the number of chromosomes in the parent cell, which is 20.
3. Chromatids in metaphase I:
Metaphase I is the stage of meiosis I where homologous chromosomes align at the center of the cell. Each replicated chromosome consists of two sister chromatids joined by a centromere. Since each chromosome in the parent cell is replicated during the S phase of interphase, the number of chromatids in metaphase I will be twice the number of chromosomes, which is 40.
4. Chromatids in prophase I:
Prophase I is the first and longest stage of meiosis I. During this stage, the chromosomes condense, and homologous chromosomes pair up. Each paired chromosome is made up of two sister chromatids, so the number of chromatids in prophase I will also be twice the number of chromosomes, which is 40.
5. DNAs in anaphase:
During anaphase of meiosis I, the homologous chromosomes separate and move towards opposite poles of the cell. The DNA in each replicated chromosome is divided equally between the two daughter cells. Since each chromosome consists of two sister chromatids, the number of DNAs in anaphase will be twice the number of chromosomes, which is 40.
6. DNAs in prophase II:
Prophase II is the first stage of meiosis II, where the nuclear envelope breaks down, and the spindle apparatus forms. Meiosis II follows meiosis I without any DNA replication. Therefore, the number of DNAs in prophase II will be the same as the number of chromosomes in meiosis I, which is 20.
In summary:
- Chromosomes in telophase II: 20
- Chromosomes in G2: 20
- Chromatids in metaphase I: 40
- Chromatids in prophase I: 40
- DNAs in anaphase: 40
- DNAs in prophase II: 20