细胞生物学英文课件-mitosis and meiosis

1、5 The observation of the stages of mitosis and meiosis 5.1 Aim of this class Understand the stages of mitosis and meiosis. 5.2 Mitosis and meiosis5.2.1 Overview of cell division Mitosis is the type of cell division that occurs in somatic cells and results in the production of two genetically identic

2、al daughter cells. Meiosis occurs in gamete formation (e.g. sperm and ova). Each daughter cell contains half the genetic information of the parent cell and crossing-over ensures a reassortment of genetic material between the chromosomes of each homologous pair. 5.2.2 Mitosis 2n2n. Prophase There is

3、condensation of chromosomes and the centrioles duplicate and migrate towards opposite poles of the cell. The nucleolus disappears. A spindle of microtubules is formed simultaneously. Dissolution of the nuclear membrane marks the end of prophase. Metaphase The chromosomes become attached to the spind

4、le. The area of attachment is called the kinetochore. The chromosomes become arranged along the spindle, forming the equatorial plate. Anaphase Chromatids separated at the centromeres and are pulled to opposite poles by the spindle. The end of anaphase is marked by the clustering of two groups of id

5、entical chromatids of opposite poles of the cell. Telophase The chromosomes begin to uncoil. The nuclear membrane re-forms and nucleoli reappear. The cytoplasm is divided into two by the process of cytokinesis. Two identical diploid daughter cells are formed as a result of mitosis. 5.2.3 Meiosis 2nn

6、. Meiosis Prophase There are five stages during which homologous chromosomes come together and exchange segments in homologous recombination: Leptotene Spindle forms. Zygotene Homologous chromosomes pair, shorten, and thicken, and form bivalents (pairs of homologous chromosomes). Pachytene Chiasmata

7、 begin to form. Chiasma is the X-shaped connection visible between paired homologous chromosomes. These become points of “crossing-over” between the chromatids. Diplotene Exchange of genetic material in chiasmata. Diakinesis Recombinant chromosomes are formed and the nuclear membrane disappears. hom

8、ologous crossing-over genetic chromosomes recombination pair Metaphase Like mitotic metaphase, chromosomes become attached to a spindle. Anaphase The chromatids do not separate and the homologous chromosomes are pulled by the spindle fibers toward opposite poles of the cell. So only half of the orig

9、inal number of chromosomes migrate toward each pole. The chromosomes migrating toward each pole thereby consist of one member of each pair of autosomes and one of the sex chromosomes, hence “reduction division”. Telophase Two genetically different daughter cells are formed. These cells contain only one member of each pair of homologous chromosomes. Meiosis The second division is like mitosis. The chromatids separate in anaphase . Meiosis gene