生物减数和有丝1（Biological reduction and filament 1）.doc

生物减数和有丝1（Biological reduction and filament 1） Two secondary spermatocytes undergo second meiotic divisions to become four sperm cells, and sperm cells must undergo a complex series of morphological changes to become spermatozoa. As a result, a spermatogonia undergoes meiosis and metamorphosis and eventually becomes the four sperm. 3. a secondary oocyte undergoes second meiotic divisions into an egg cell and a polar body; a polar body resulting from the first division is subdivided into two polar bodies. Soon, the three polar bodies will degenerate and disappear. As a result, an egg cell undergoes meiosis and eventually becomes an egg cell. Chromosome, DNA, chromatid, homologous chromosome, logarithm Intervals are 2N, 2N, 4N, 0, 4N, N Prophase I, 2N, 4N, 4N, N Metaphase I, 2N, 4N, 4N, N Anaphase I, 2N, 4N, 4N, N End I, 2N, N, 4N, 2N, 4N, 2N, N, 0 Prophase II, N, 2N, 2N, 0 Metaphase II, N, 2N, 2N, 0 Anaphase II, N, 2N, 2N, 2N, 0, 0 End II, N, N, 2N, N, 0, 0 The number of centromere is consistent with the number of chromosomes Meiosis is a specific division of sex cells. In the life history of all sexually transmitted organisms, cells undergo a meiotic division in addition to several mitosis, resulting in the number of chromosomes changing from diploid (2n) to haploid (n). Because meiosis allows each organism to maintain diploid chromosome numbers from generation to generation. Meiosis consists of two successive divisions, termed meiosis I and meiosis ii. Between these two divisions, there is usually a very short interval, without DNA synthesis, and thus no chromosomal duplication occurs. Since the nucleus divides two times and the chromosomes replicate only once, the number of chromosomes is halved by meiosis. Meiosis prophase I is complex, and many special processes of meiosis occur during this period. It is subdivided into: Fine line. Chromatin has been condensed into elongated threadlike structures, each of which is connected to the nuclear membrane by attaching th