Biology lecture 7 how cell divided cell division 2
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Meiosis is a type of cell division that produces gametes, such as sperm and egg cells, with half the normal number of chromosomes. It involves two rounds of cell division called Meiosis I and Meiosis II. In Meiosis I, homologous chromosome pairs separate and are distributed into two daughter cells. Meiosis II then separates the sister chromatids, resulting in four haploid daughter cells each with a single set of chromosomes. This ensures genetic diversity in the next generation.
Biology lecture 7 how cell divided cell division 2
- 1. 8- How cell divided cell division 11 Meiosis; Reduction division Dr. Siham Gritly University of Bahri Dr. Siham Gritly 1
- 2. Meiosis; Reduction division That Occurs in Sexually Reproducing Organisms • Part of the process of gamete formation, • consisting of chromosome conjugation and two cell divisions, in the course of which the diploid chromosome number becomes reduced to the haploid. • Diploid cells have two homologous copies of each chromosome. Dr. Siham Gritly 2
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- 4. • Meiosis is used only for the production of sperm and eggs Dr. Siham Gritly 4
- 5. Meiosis has two unique features: synapsis and reduction division. • 1- Synapsis • * The process of pairing throughout the length of the homologous chromosomes and exchanging genetic fragments is called synapsis. Dr. Siham Gritly 5
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- 7. • 2-Reduction Division • Reduction division: The first cell division in meiosis, the process by which germ cells are formed. • In reduction division, the chromosome number is reduced from diploid (46 chromosomes) to haploid (23 chromosomes) Dr. Siham Gritly 7
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- 9. Meiosis features • -yields genetically unique haploid daughter cells (cells with only one member of each homologous chromosome pair). • -involves 2 nuclear and cytoplasmic divisions • -produces 4 haploid cells Dr. Siham Gritly 9
- 10. The Sexual Life Cycle Dr. Siham Gritly 10 1. In the sexual life cycle, there is an alternation of diploid and haploid generations. 2. Normal diploid body cells are called somatic cells. 3. Somatic cells arise from the zygote and are all genetically identical.
- 11. Germ-Line Tissues Dr. Siham Gritly 11 1. Cells that produce gametes are called germ-line tissues. 2. Germ-line cells will undergo meiosis to produce haploid gametes.
- 12. The stages of meiosis can be broken down into two main stages, Meiosis I and Meiosis II • A. Meiosis I can be broken down into four substages: • Prophase I, • Metaphase I, • Anaphase I • and Telophase I • Meiosis I serves to divide the two versions of each chromosome; Dr. Siham Gritly 12
- 13. • B. Meiosis II can be broken down into four substages: • Prophase II, • Metaphase II, • Anaphase II • and Telophase II • meiosis II separates the two replicas of each chromosome. Dr. Siham Gritly 13
- 14. Meiosis I • The first cell division in Meiosis is known as Meiosis I. • The function of Meiosis I is very different from that of either Mitosis or Meiosis II. • In both Mitosis 1 and Meiosis II sister chromatids are separated during anaphase to produce identical daughter cells. Dr. Siham Gritly 14
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- 16. • In Meiosis I members of homologous chromosome pairs are separated. • This results in the segregation of genes into the two gametes. Dr. Siham Gritly 16
- 17. stages of Meiosis I : • 1-prophase I occurs as the chromosomes condense, homologues pair, and crossing over occurs; • Prophase; Main event in prophase of M1 is “crossing over”, also called “recombination”. Dr. Siham Gritly 17
- 18. • In crossing over, homologous chromosomes pair up, and exchange segments by breaking and rejoining at identical locations. • ( Crossing over allows for combinations of genes that may never have existed previously). Dr. Siham Gritly 18
- 19. Crossing over allows for combinations of genes that may never have existed previously Dr. Siham Gritly 19
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- 21. • 2-metaphase I involves formation of the spindle apparatus and alignment of chromosome pairs along the center of the cell; Dr. Siham Gritly 21
- 22. • 3-anaphase I, The centromeres break and homologous chromosomes separate and pulled toward the poles (note that the sister chromatids are still attached) • Cytokinesis begins Dr. Siham Gritly 22
- 23. • 4-telophase I, the chromosomes gather at each pole and prepare for the second division. • cleavage furrow formed • Cytokinesis reaches completion, creating two haploid daughter cells Dr. Siham Gritly 23
- 24. Meiosis II • Meiosis II, which also has four stages, follows after meiosis I, • This result is the separation of the sister chromatids to form four haploid gametes. Dr. Siham Gritly 24
- 25. 4 stages of meiosis11 • * prophase 11, the chromosomes condense and the spindle forms. • Centrioles form and move toward the poles • The nuclear membrane dissolves Dr. Siham Gritly 25
- 26. • *Metaphase 11; chromosomes line up singly on the cell equator. • Microtubules grow from the centrioles and attach to the centromeres • The sister chromatids line up along the cell equator Dr. Siham Gritly 26
- 27. • *Anaphase 11; centromeres divide and pulled to opposite poles. • The centromeres break and sister chromatids separate • Cytokinesis begins Dr. Siham Gritly 27
- 28. • *telophase 11; cytoplasm divided into 2 cells. • The chromosomes may decondense • Cytokinesis reaches completion, creating four haploid daughter cell Dr. Siham Gritly 28
- 29. Cytokinesis • the cytoplasmic division of a cell at the end of mitosis or meiosis, bringing about the separation into two daughter cells. • The division of the cytoplasm and the plasma membrane following the division of the nucleus resulting into two cells, each having its own nucleus and cytoplasm surrounded by a plasma membrane. • This process begins during the late stage of mitosis (Telophase) and meiosis (Telophase II). Dr. Siham Gritly 29
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