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Understanding Meiosis: The Process of Gamete Formation and Genetic Diversity

Meiosis is a specialized type of cell division essential for sexual reproduction, converting one diploid cell (46 chromosomes) into four haploid gametes (23 chromosomes each). This process occurs in male and female gonads (testes and ovaries) and is crucial for ensuring genetic diversity through mechanisms such as crossing over and independent assortment. During meiosis, homologous chromosomes pair up, exchange genetic information, and separate, forming unique combinations that contribute to the genetic makeup of offspring. Ultimately, this process is vital for creating the zygote during fertilization, ensuring a variety of genetic contributions from both parents.

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Understanding Meiosis: The Process of Gamete Formation and Genetic Diversity

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  1. Meiosis 11.4

  2. Homologous Chromosomes • Homologous chromosomes: pairs of chromosomes with genes for the same traits, but they can have different information about those traits

  3. Humans • Humans have 46 chromosomes or 23 pairs of homologous chromosomes. • Somatic(body) cells contain 46 chromosomes. • 46 is the diploid number for humans. - Diploid means that a cell has both homologs for each chromosome • Somatic cells reproduce by mitosis

  4. ½ the chromosomes in a cell come from Mom, ½ the chromosomes in a cell come from Dad

  5. The Homolog’s

  6. Reproductive Cells • Gametes(eggs and sperm) are called haploid because they contain one set of chromosomes. • Eggs also called Ovum and sperm contain 23 chromosomes. • @Eggs and sperm are produced by meiosis- a process that reduces chromosomes by half@

  7. What is Meiosis? • A type of cell division where ONE diploid cell (46 chromosomes) become FOUR haploid cells(23 chromosomes each). • The cells produced by meiosis are gametes (sex cells)

  8. One diploid cell gives rise to 4 haploid cells 46 23 23 23 23

  9. Who does it? • Plants • Fungi • Animals (including you) • Males start meiosis at puberty. • Females start meiosis in utero.

  10. Where does it occur? • In your gonads • Females- the ovary • Males-the testicles

  11. Why does it occur? • Genetic Variation • Mixes genes from Mom and Dad to create a unique baby • @Reduces the chromosome number by half@ • Ensures that each cell produced has one copy from each homologous pair of chromosomes • 23 in sperm + 23 in egg unite (fertilization) leads to a 46 zygote(baby)

  12. Meiosis creates the cells needed for sexual reproduction • Two haploid gametes join to form one diploid cell. - the new diploid cell (fertilized egg) is called a zygote

  13. How does it occur? • In two stages called Meiosis I and Meiosis II. • Each stage contains 4 distinct phases prophase metaphase anaphase teleophase telophase is followed by the division of cytoplasm known as cytokinesis.

  14. Prophase 1 • Homologouschromosomes join to form a tetrad -chromosomes in the tetrad cross over and exchange genes

  15. @Crossing over produces new genetic combinations@ - It is another way to increase genetic diversity

  16. Metaphase 1 • During Metaphase 1, the tetrads (groups of 4 homologous chromosomes) line up down the center of the cell - they assort independently -Chromosomes from each parent line up independently of each other

  17. Anaphase I • During anaphase I, spindle fibers pull each homologous chromosome pair toward opposite ends of the cell. • When anaphase I is complete, the separated chromosomes cluster at opposite ends of the cell.

  18. Telophase I and Cytokinesis • During telophase I, a nuclear membrane forms around each cluster of chromosomes. • Cytokinesis follows telophase I, forming two new cells.

  19. Meiosis II • @The two cells produced by meiosis I now enter a second meiotic division. @ • Unlike the first division, neither cell goes through a round of chromosome replication before entering meiosis II.

  20. Prophase II • As the cells enter prophase II, their chromosomes—each consisting of two chromatids—become visible. • The chromosomes do not pair to form tetrads, because the homologous pairs were already separated during meiosis I.

  21. Metaphase II • During metaphase of meiosis II, chromosomes line up in the center of each cell.

  22. Anaphase II • As the cell enters anaphase, the paired chromatids separate.

  23. Telophase II, and Cytokinesis • These four daughter cells now contain the haploid number (N)—just two chromosomes each.

  24. Independent Assortment • @Independent assortment increases genetic diversity@ - There are 23 pairs of homologous chromosomes in humans - independent assortment ensures that there are 223 possible combinations 223= 8,388,608 combinations - When two gametes join to form the zygote in fertilization the possible number of combinations is 223 X 223 = 64 trillion

  25. Independent Assortment

  26. What happens in prophase I that produces new genetic combinations? • Crossing over

  27. How many chromosomes do human sperm/eggs have? • 23 chromosomes

  28. How is mitosis different from meiosis? • Mitosis creates 2 daughter cells with same amount of chromosomes • Meiosis creates 4 daughter cells with half amount of chromosomes • Meiosis goes through 2 cycles

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