生物必修二2（Biology required two 2）.docVIP

生物必修二2（Biology required two 2） The second chapter is the relationship between genes and chromosomes The first division of meiosis and fertilization First, the concept of meiosis Meiosis is the mode of cell division characterized by the formation of reproductive cells during sexual reproduction. During meiosis, the chromosomes replicate only once, and the cells divide two times, and the number of chromosomes in the newly created germ cells is less than half of that in somatic cells. (Note: somatic cells are produced mainly by mitosis. During mitosis, chromosomes replicate once, and cells divide at once. The number of chromosomes in newly created cells is the same as that in somatic cells Two. The process of meiosis 1, sperm formation process: testis (mammal called testis) Meiosis, first division Interphase: replication of chromosomes (including DNA replication and protein synthesis). Prophase: 22 pairs of homologous chromosomes (called associations) forming four bodies. The exchange of reciprocal fragments often occurs between four sister chromatid pairs. Metaphase: homologous chromosomes are arranged in pairs on the equatorial plate (both sides). Anaphase: homologous chromosome segregation; non homologous chromosome free combinations. Telophase: the division of cytoplasm into 2 daughter cells. Meiosis second division (without homologous chromosomes) Prophase: the arrangement of chromosomes is scattered. Metaphase: the centromere of each chromosome is arranged on the equatorial plate at the center of the cell. Anaphase: sister chromatid divided into two stripe chromosomes. And move to the cell poles respectively. Telophase: cytokinesis divides each cell into 2 daughter cells and ends up forming 4 daughter cells. 2. The process of egg formation: ovary Three. Comparison of the formation of sperm and egg cells The formation of sperm; the formation of eggs Testes formed at different points (testes, testes), ovaries The process has a deformation period without deformation