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Understanding Meiosis in Sexual Reproduction

Learn the vocabulary, stages, and importance of meiosis in sexual reproduction. Explore germ cells, haploid and diploid cells, gametes, and more. Understand how meiosis creates genetic variability and the impact of non-disjunction.

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Understanding Meiosis in Sexual Reproduction

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  1. MEIOSIS

  2. Meiosis is required for Sexual Reproduction

  3. Vocabulary List • Germ Cell • Haploid (1n) • Diploid (2n) • Gamete • Zygote • Somatic Cell • Sex Cells • Chromatid • Chromosomes • Homologous Pair • Crossing Over

  4. “histones” are wound up like rope DNA strands get wrapped around proteins called “histones” DNA “Rope” is twisted and stacked to create chromosomes during Prophase What is a chromsome?

  5. Germ Cells • Cells that undergo meiosis are called germ cells. • Human male germ cells are located in the testes • Human female germ cells are located in the ovaries

  6. Diploid Having 2 copies of each chromosome (2n) • One maternal copy and one paternal copy All body cells are diploid Example: skin cells or stomach cells Haploid Having 1 copy of each chromosome (1n) Example: Sperm and Ovum (Egg Cells)

  7. Somatic Cell A body cell that has two sets of chromosomes Gamete A reproductive cell that has only 1 set of chromosomes (1n) Example: Sperm or Egg Zygote a fertilized egg with 2 sets of each chromosome (2n)

  8. Sexual reproduction involves the fusion of male and female gametes. • The resulting cell is called a zygote.

  9. Image of Chromosomes • All of our cells (except gametes) have 2 copies of each chromosome. • One copy of each chromosome is maternal, and the other copy is paternal.

  10. Single Chromatid from the father Single Chromatid from the mother Duplication Duplication

  11. Homologous Chromosome Pair • 1 from mother and 1 from father • Carry genes for the same trait • Can be different for each chromosome in pair • Example: Eye color (blue vs. brown)

  12. One Homologous Pair of Chromosomes

  13. Meiosis Type of cell division that cuts the number of chromosomes in half • involves 2 divisions: • (meiosis I & meiosis II) • occurs in germ cells • It’s how we get our sex cells (gametes)

  14. Meiosis starts with 1 diploid cell and produces 4 haploid cells 1 diploid 4 haploid cells

  15. Meiosis I Meiosis II

  16. Prophase I Events are the same as prophase in Mitosis • replicated chromosomes condense • spindle apparatus forms & fibers attach to chromosomes • nuclear membrane breaks down • New EVENT for Prophase I • synapsis & crossing over occurs

  17. Synapsis when homologous chromosomes pair up

  18. Crossing Over Non-sister chromatids exchange chromosome material Chromatids exchange pieces of chromosome material

  19. Metaphase I • Same as Metaphase in Mitosis except.. • Homologous Pairs of Chromosomes line up along the equator (known as a tetrad) • Chromosomal orientation is random

  20. Anaphase I Homologous chromosomes separate & move to opposite poles

  21. Telophase I • spindle apparatus breaks down • chromosomes decondense • nuclear membranes partially reform around two nuclei Cytokinesis occurs between meiosis I & II

  22. Meiosis II Each of the 2 cells formed by Meiosis I proceed to Meiosis II • Looks EXACTLY like Mitosis!!! • Prophase II • Metaphase II • Anaphase II • Telophase II and Cytokinesis

  23. Meiosis II • Prophase II • chromosomes condense • spindle fibers form • nuclear membrane breaks down • Metaphase II • chromosomes line up single-file along equator of spindle • Random orientation of chromosomes

  24. Meiosis II Anaphase II • sister chromatids (now called chromosomes) separate & move toward opposite poles Telophase II • spindle fibers break down • chromosomes de-condense • nuclear membranes reform Cytokinesis divides the 2 cells into 4

  25. How does Meiosis Apply to me? • We all have 46 Chromosomes in each of our somatic (body) cells • Mother’s Egg – produced by Meiosis and has 23 Chromosomes (haploid) • Father’s Sperm – produced by Meiosis and has 23 chromosomes (haploid) • Egg fertilized by Sperm  46 Chromosomes in a zygote (Diploid)

  26. Male vs. Female Meiosis • Creation of male gametes through meiosis is called spermatogenesis. • Result is 4 sperm cells • Males create sperm continuously throughout their entire lifespan. • Creation of female gametes (ovum or egg cells) is called oogenesis. • Result is one viable egg cell • Women are born with all the eggs they will have. When they run out, this is known as menopause

  27. Exit Ticket • A horse skin cell has 64 chromosomes. What is a horse’s haploid number? 32 • A fruit fly’s liver cell has 4 pairs of chromosomes. How many chromosomes are in a fruit fly sperm cell? 4

  28. Exit Ticket • What are two ways that meiosis produces genetic variability? • Crossing over • Random orientation of chromosomes • When do these mechanisms take place? • Crossing over- Prophase I • Random orientation- Metaphase I

  29. Non-Disjunction • Chromosomes may fail to separate during anaphase 1 or when chromatids fail to separate during anaphase II of Meiosis • Resulting gametes may have too few or too many chromosomes

  30. Results of Non-disjunction

  31. Results of Non-disjunction

  32. Regulation of Cell Cycle • The advancement of stages of the cell cycle is regulated by a family of chemicals called Cyclins.

  33. Lack of Regulation • Cancer tumors is the result of unregulated mitosis. • These cells do not respond to cyclin regulation and divide rapidly and constantly.

  34. Formation of cancerous tumor

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