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Sagot :
Answer:
a. 6.0 x 10^-12 g.
Explanation:
The interphase is the previous step before the cell divission occurs. The interphase is formed of the G1, S, and G2 stages.
• During the G1 stage, it occurs a high intense biochemical activity. The cell duplicates its size, and the organelles and other molecules and cytoplasmatic structures duplicate too. Some structures, such as microtubules and actin filaments, are synthesized from zero. The endoplasmic reticulum increases in size and produces a membrane for the Golgi apparatus and vacuoles, lysosomes, and vesicles. During this stage, the pair of centrioles separate, and each centriole duplicates. Mitochondria and chloroplasts also replicate.
• During the S stage occurs the DNI replication process. It also occurs the synthesis of histones and other associated proteins. This is the only stage where the DNI molecule is replicated.
• G2 stage is the final one before the cellular division. Here begins the slow process of DNI condensation. Duplication of centrioles completes. Structures such as spindle fibers are assembled.
Through the process of Meiosis, a diploid germ cell (2n) divides and originates four daughter cells with a haploid chromosome number (n). Each daughter cell has half of the chromosomes of the original one. Meiosis is completed in two phases. During the first phase, and after replication, occurs the chromosome´s reduction division. During the second phase, the cell suffers a new, not reductive division.
1. In the first phase, Meiosis I:
- Prophase I: Chromosomes condensate and became visible. Occurs crossing-over between homologous chromosomes. Crossin-over makes the daughter cells to be genetically different from the original one.
- Metaphase I: The pairs of homologous chromosomes randomly align in the equatorial plane.
- Anaphase I: occurs the independent separation of homologous chromosomes that migrate to opposite poles of the cell. This separation generates different chromosomal combinations in the daughter cells.
- Telophase I: Each of the homologous pairs chromosomes is already in the corresponding poles, and the nuclear membrane forms again in each pole.
2. In the second phase, Meiosis II:
- Prophase II: Chromosomes condensate again and become visible.
- Metaphase II: Chromosomes join the spindle apparatus and migrate to the equatorial plane, where they randomly line up. Sister chromatids are holden together until they reach the Anaphase.
- Anaphase II: Centromeres divide, chromatids get separated, and each of them goes forward an opposite cellular pole.
- Telophase II: Once in the poles, the chromosomes became lax again, and cytokinesis occurs.
In the exposed example, DNI in the G1 nucleus of a mosquito cell still has not suffered replication (3.0 x 10^-12 grams). The replication process occurs during the S stage, which follows the G1 stage. After the S stage, the cell has 6.0 x 10^-12 g of DNI.
During meiosis, the reduction in chromosomes number occurs in anaphase where homologous chromosomes migrate to different poles. But during metaphase I, the cell still has 6.0 x 10^-12 g of DNI.
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