For an organism that has a diploid number of chromosomes of 12, give the number of chromosome/chromatid copies at the end of the following cell-cycle phases:
a) G2 phase
b) Meiosis I metaphase
c) Meiosis II telophase
To answer this question, we need to understand the processes of the cell cycle and meiosis. Let's break it down step by step:
1) The diploid number of chromosomes refers to the total number of chromosomes in a somatic cell of the organism. In this case, the organism has a diploid number of 12 chromosomes.
2) The cell cycle has several phases, including G1 (Gap 1), S (Synthesis), G2 (Gap 2), and M (Mitosis). Meiosis, on the other hand, is a special type of cell division that occurs in reproductive cells to produce gametes.
Let's look at each phase and determine the number of chromosome/chromatid copies:
a) G2 Phase:
During G2 phase, the cell prepares for cell division. At this point, the cell still has the diploid number of chromosomes but has already replicated its DNA during the S phase. Therefore, each chromosome has two identical copies known as sister chromatids. Since the diploid number is 12, in G2 phase, there will be 12 pairs of sister chromatids, so the total number of chromosome/chromatid copies will be 24.
b) Meiosis I Metaphase:
During Meiosis I metaphase, homologous chromosomes pair up and align at the metaphase plate. This alignment forms tetrads, which consist of four chromatids. Remember that homologous chromosomes have the same genes but potentially different versions of those genes. Since there are 12 chromosomes and each chromosome has two chromatids, there will be a total of 24 chromatids in Meiosis I metaphase.
c) Meiosis II Telophase:
During Meiosis II telophase, the chromatids separate, similar to mitosis. At the end of Meiosis II, the final products are four haploid cells. Each of these cells contains half the number of chromosomes as the original cell. Since the diploid number is 12, at the end of Meiosis II telophase, each cell will have 6 chromosomes.
In summary:
a) G2 phase: 24 chromosome/chromatid copies.
b) Meiosis I metaphase: 24 chromatids.
c) Meiosis II telophase: 6 chromosomes.
Remember, understanding the concepts of the cell cycle and meiosis is crucial to answer questions like these.
a) G2 phase: The G2 phase of the cell cycle is the period after DNA synthesis has occurred during the S phase but before cell division takes place during mitosis. In the G2 phase, the cells are still diploid, meaning they have two sets of chromosomes. Therefore, the number of chromosome copies at the end of the G2 phase will be 2 copies.
b) Meiosis I metaphase: During meiosis I, the homologous chromosomes pair up and align along the equatorial plate during metaphase I. At this stage, crossing over may have occurred, leading to genetic recombination between homologous chromosomes. Each chromosome is still composed of two sister chromatids. So, the number of chromosome/chromatid copies will be 12 pairs of replicated chromosomes, resulting in 24 chromatid copies.
c) Meiosis II telophase: In meiosis II, the separated sister chromatids from the previous division will now undergo another round of cell division. During telophase II, the sister chromatids reach opposite poles of the cell and nuclear envelopes start to form around each set of chromosomes. At this stage, the number of chromosome/chromatid copies will still be 12, but the chromatids will be unreplicated. This means that there will be 12 unreplicated chromosomes.