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Cell Division and Reproduction

This comprehensive overview details the mechanisms of cell division, focusing on asexual and sexual reproduction. Asexual reproduction involves a single organism producing identical offspring, while sexual reproduction requires the fusion of haploid sperm and egg cells to form a diploid zygote. The process of meiosis is explored in depth, including its phases and significance in genetic variability through crossing over. Additionally, the differences between mitosis and meiosis are highlighted, illustrating the production of gametes and the genetic diversity among offspring.

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Cell Division and Reproduction

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  1. Cell Division and Reproduction Asexual and Sexual reproduction By : D. Reis

  2. Asexual Reproduction • A single organism produces offspring with identical genetic information

  3. Sexual Reproduction • Haploid (n=23) sperm cell fertilizes a haploid (n=23) egg cell to produce a dipolid (2n=46) zygote.

  4. Sexual Reproduction • Cells of the human body have 46 chromosomes • When fertilization occurs a sperm and egg cell combine their chromosomes to make a zygote with 46 chromosomes. • How is this possible?

  5. Meiosis • The division of cells to produce specialized sperm and egg cells 46 23 23 23 23 23 23

  6. Phases of Meiosis • Assume DNA replication occurs prior to meiosis I • Prophase I • Metaphase I • Anaphase I • Telophase I • Prophase II • Metaphase II • Anaphase II • Telophase II

  7. Homologous Chromosomes • Paired chromosomes similar in shape, size, gene arrangement and gene information. • Each somatic cell contains 23 pairs of homologus chromosomes, or 46 in total

  8. Stages of Meiosis I PROPHASE I – • Nuclear membrane dissolves • Centrioles move to opposite poles • Formation of spindle fibers

  9. Stages of Meiosis I • PROPHASE I- Homologus chromosomes pair up in a process called synapsis and crossing over occurs

  10. Crossing Over/ Genetic Recombination • The exchange of genetic material between two homologus chromosomes leads to genetic variability. • Tetrad – a pair of homologus chromosomes composed of 4 chromatids.

  11. Stages of Meiosis I • METAPHASE I- Homologus chromosomes line up at the equatorial plate.

  12. Stages of Meiosis I • ANAPHASE I- Spindle fibers shorten, the homologus chromosome pairs move toward opposite poles. THE SISTER CHROMATIDS DO NOT PULL APART AS THEY DO IN MITOSIS. • 23 duplicated chromosomes move to opposite poles. • TELOPHASE I- Two new genetically different haploid daughter cells are formed each containing 23 double stranded chromosomes • Formation of nuclear membrane

  13. Stages of Meiosis II • PROPHASE II – Nuclear membrane dissolves, spindle fibers form and centrioles move to opposite poles. • METAPHASE II – Spindle fibers attach to the chromosomes and the chromosomes (2 sister chromatids) align along the equatorial plate.

  14. Stages of Meiosis II • ANAPHASE II – Sister chromatids separate and move to opposite poles. • TELOPHASE II – Chromatids arrive at each pole and cell division begins.

  15. Meiosis 1. Homologus chromosomes: 23 paternal and 23 maternal 2. Chromosomes are replicated and attached at the centromere

  16. Meiosis 3. Meiosis I reduction stage- Separation of homologus chromosomes 4. Meiosis II- separation of sister chromatids

  17. Results of Meiosis • 4 gametes/reproductive cells which contain 23 chromosomes • Haploid-each cell contains half the number of chromosomes from the parent cell • All 4 cells are genetically different

  18. Results of Meiosis

  19. Results of Meiosis • Oogenesis- the production of egg cells in females • Spermatogenesis- the production of sperm cells in males

  20. Mitosis and Meiosis Compared

  21. Mitosis 2 daughter cells are produced Daughter cells are diploid Daughter cells are the same as parent cells Meiosis 4 daughter cells are produced Daughter cells are haploid Daughter cells are genetically different from parent cells Mitosis and Meiosis Compared

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