![]() Analysis of single-cell transcriptomics data from human fetal germ cells (FGC) allowed us to identify the molecular signatures of female meiotic prophase I stages leptotene, zygotene, pachytene and diplotene. Therefore, it remains unclear how the different stages of meiotic prophase I between human oogenesis and spermatogenesis compare. Hence, the knowledge regarding progression through meiotic prophase I is mainly focused on human male spermatogenesis and female oocyte maturation during adulthood. In contrast to males, meiotic prophase I in females initiates during development. The timing and length of meiosis to produce female and male gametes differ considerably. Prophase II is essentially the same as mitotic prophase except that the cells are haploid.During gametogenesis in mammals, meiosis ensures the production of haploid gametes. During _ a spindle forms in a haploid cell. At the end of _ and cytokinesis there are four haploid cells.Īt the end of telophase II and cytokinesis there are four haploid cells. Metaphase II is essentially the same as mitotic metaphase except that the cell is haploid. During _ chromosomes align single file along the equator of a haploid cell. Part F Homologous chromosomes migrate to opposite poles during _.ĭuring anaphase I sister chromatids remain attached at their centromeres, and homologous chromosomes move to opposite poles. Synapsis, the pairing of homologous chromosomes, occurs during prophase I. At the end of _ and cytokinesis, haploid cells contain chromosomes that each consist of two sister chromatids.Īt the end of telophase I and cytokinesis, there are two haploid cells with chromosomes that consist of two sister chromatids each. During _ sister chromatids separate.Īnaphase II is essentially the same as mitotic anaphase except that the cell is haploid. Meiosis II typically produces _ cells, each of which is _.Īt the end of meiosis II there are typically 4 haploid cells. If we continued to follow the cell lineage, the DNA content of a cell at metaphase of meiosis II would be _.Ģx x Meiosis I produces _ cells, each of which is _.Īt the end of meiosis I there are two haploid cells. Prophase II Prophase I If the DNA content of a diploid cell in the G1 phase of the cell cycle is represented by x, then the DNA content of the same cell at metaphase of meiosis I would be _.Ģx 2x If the DNA content of a diploid cell in the G1 phase of the cell cycle is represented by x, then the DNA content of the same cell at metaphase of meiosis I would be 2x. Crossing over between the two homologs of a pair occurs in a dividing cell during _. With crossing over, however, all four daughter cells are genetically unique. Without crossing over, sister chromatids remain identical and thus, pairs of daughter cells would be identical. The effect of crossing over on genetic variation is shown below. The independent assortment of homologous chromosomes (which are never identical) in meiosis I produces daughter cells that differ from each other. ![]() However, crossing over is not the only process that introduces genetic variation in meiosis I. ![]() This is because the exchange of maternal and paternal genes between the nonsister chromatids of a homologous chromosome pair creates recombinant chromosomes with unique combinations of alleles. * There would be less genetic variation among gametes.Ĭrossing over contributes significantly to the genetic variation seen in gametes. * The daughter cells of meiosis I would be diploid, but the daughter cells of meiosis II would be haploid. * There would be less genetic variation among gametes. * The two sister chromatids of each replicated chromosome would no longer be identical. * The four daughter cells produced in meiosis II would all be different. * The two daughter cells produced in meiosis I would be identical. * Independent assortment of chromosomes would not occur. If crossing over did not occur, which of the following statements about meiosis would be true? Select all that apply. Consider how the absence of crossing over would affect the outcome of meiosis. Assume that an organism exists in which crossing over does not occur, but that all other processes associated with meiosis occur normally.
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