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Meiosis & Sex Cell Reproduction

Most animals reproduce through sexual reproduction that involves combining genetic material from two parents (sperm and egg) to produce genetically different offspring. Meiosis is the process where sex cells are formed, reducing the chromosome number to maintain genetic diversity indispensable for life. This article explains the intricate phases of meiosis contrasting it with mitosis, ensuring a clear comprehension of cell reproduction. Explore how cells divide and reproduce in all living organisms through both somatic and sex cell replication.

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Meiosis & Sex Cell Reproduction

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  1. Write Meiosis & Sex Cell Reproduction

  2. ALL LIVING THINGS reproduce Most animals undergo SEXUAL REPRODUCTION Combinesgenetic material from 2 parents (sperm & egg) so offspring are genetically different from parents

  3. Review Before we learn about sex cell reproduction, let’s revisit somatic cell reproduction…mitosis • Mitosis • occurs in somatic (body) cells • Includes all cells exceptsex cells(eggs and sperm) • produces cells with same genetic information • identical daughter cells • same number of chromosomes in all cells

  4. Think 46 46 23 23 46 23 23 Why must sex cells(aka gametes) be different? • Human cells contain 46 chromosomes • If an egg with 46 chromosomes joins with a sperm with 46 chromosomes how many chromosomes would the offspring have? • If that process continued, after 10 generations human cells would have 46 X 210 chromosomes… • YIKES!!!!! To prevent exponential growth in chromosomes, sex cells must reduce 46 chromosomes (diploid) to 23 (haploid) egg zygote meiosis sperm fertilization

  5. Write diploid = 2 copies aka Homologous chromosomes (1 from mother/1 from father) 46 chromosomes (diploid) is same as 23 pairs 23 chromosomes (haploid) 2n n

  6. How does meiosis occur? Write • Two stages called Meiosis I and Meiosis II. • Each stage contains 4 distinct phases: Prophase I, Metaphase I, Anaphase I, Telophase I Prophase II, Metaphase II, Anaphase II, Telophase II Telophase is followed by division of cell cytoplasm (aka cytokinesis).

  7. Write • Interphase: • Same as mitosis • Protein synthesis • Cell growth • Organelles made • DNA copied (chromatin)

  8. Interphase I

  9. Prophase I Write • Chromosomes formed and paired with corresponding homologous chromosome to form a tetrad. • 4 chromosomes (2 sister chromatids each) in a tetrad. • DNA sections from chromatids unwind and pair with corresponding homologue • Crossing-over may occur • chromosomes overlap and exchange portions of their chromatids • produces new genetic combinations tetrad MOM DAD

  10. Prophase I

  11. Write Metaphase I • Pairs of homologous chromosomes line up together in the middle of the cell • Alignment is random (called independent assortment) • Spindle fibers form

  12. Metaphase I

  13. Write Anaphase I • Spindle fibers pull one chromosome of each homologous pair to opposite poles of the cell • Now haploid (1 chromosome of the original pair)

  14. Anaphase I

  15. Write Telophase I & Cytokinesis • Haploid chromosomes gatherat each pole • Each chromosome is made of two chromatids that are not identical due to crossing over during Prophase I • Two haploid cells form

  16. Telophase 1

  17. Meiosis II • Meiosis II is just like Mitosis. • Prophase II: the chromosomes condense and the spindle fibers form. • Metaphase II: chromosomes (non-identical chromatids) line up singly in the middle of the cell. • Anaphase II: chromatids get pulled to opposite poles by spindle fibers. • Telophase II: cytoplasm divides into 2 cells. • After Meiosis II: total of 4 cells from the original cell. • Each contains one haploid set of chromosomes

  18. Write The value of Meiosis • Keeps chromosome number same from generation to generation • 1 diploid cell creates 4 haploid cells • Introduces genetic variation • crossing over (Prophase I) • independent assortment (Metaphase I)

  19. Write Mitosis vs Meiosis 2 Diploid Cells (2n) 4 Haploid Cells (1n) Different Identical Somatic (Body) Cells Sex Cells

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