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Meiosis and Gamete Formation

Dive into the intricate process of meiosis and gamete formation to uncover how sex cells are created from germline cells via meiosis. Discover the vital role of male (sperm) and female (oocyte) gametes in forming new individuals and the significance of genetic diversity. Explore the phases of meiosis, from Prophase I to Telophase II, and how independent assortment leads to new combinations of genetic information. Gain insights into spermatogenesis and oogenesis in the male and female reproductive systems, respectively.

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Meiosis and Gamete Formation

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  1. Meiosis and Gamete Formation

  2. Gametes • Gametes =sex cells • Gametes form from germline cells via meiosis • Male gamete =sperm • Female gamete =oocyte (egg) • A male and a female gamete come together to form a new individual • Somatic (non-gamete) cells have 46 chromosomes (diploid) • Gametes have 23 chromosomes (haploid) • ½ + ½ = 1 whole

  3. Human Karyotype

  4. Remember… Replicated chromosome (2 sister chromatids connected at centromere) A chromosome Figure 3.2 Homologous pair of replicated chromosomes Homologous pair of chromosomes

  5. from mother from father child too much! Meiosis • Produces gametes (1n or haploid) from somatic germline cells (2n or diploid) meiosis reduces genetic content Figure 3.1

  6. Meiosis I (reduction division) Meiosis II (equational division) Diploid Haploid Haploid Meiosis Meiosis overview • Produces gametes (1n or haploid) from somatic germline cells (2n or diploid) • Mixes up genetic information • Diversity is important! • Consists of 2 divisions • Meiosis I • Meiosis II Figure 3.1

  7. Meiosis I • Interphase (CHROMOSOMES REPLICATE) • Prophase I • Metaphase I • Anaphase I • Telophase I

  8. Interphase • Precedes Meiosis I • Cell grows and organelles are made • CHROMOSOMES ARE REPLICATED Homologous pair of replicated chromosomes Homologous pair of chromosomes

  9. Prophase I • Pro =forward, forth • Chromosomes condense • Nuclear envelope breaks down • Membrane surrounding the nucleus • Centrioles move to opposite poles • Spindle fibers grow • Chromosomes synapse and crossing over occurs Q4 Prophase

  10. Crossing Over (Recombination) Q7 • Replicated chromosomes pair up with their homologs • i.e. chromosome from mom and chromosome from dad get together • Genetic information is exchanged • Like shuffling a deck of cards and re-dealing Homologous pair of replicated chromosomes New combinations of genetic info Synapsis

  11. Metaphase I Q4 Metaphase • Meta =after, with • Homologous chromosome pairs line up at the midline • Line up is random so that INDEPENDENT ASSORTMENT takes place • Spindle attaches to chromosomes at the centromere • The centromere is where the sister chromatids are attached

  12. Independent Assortment • Another way in which meiosis increases diversity • Chromosomes line up at the midline in a random way Q3

  13. Anaphase I • Ana =against • Homologous pairs split • Homologs are pulled to opposite poles by the shortening of spindle fibers Q4 Anaphase

  14. Telophase I • Telo =completion of a goal • Spindle breaks down • Nuclear envelope forms in each of the new cells Q4 Telophase

  15. Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (diploid) Telophase I (diploid) Summary of Meiosis I INTERPHASE

  16. Meiosis II • Interphase –Chromosomes DO NOT replicate! • Prophase II • Metaphase II • Anaphase II • Telophase II

  17. Prophase II • Nuclear envelope breaks down • Membrane surrounding the nucleus • Centrioles move to opposite poles • Spindle fibers grow Q4 PII

  18. Metaphase II • Chromosomes line up at the midline • Spindle attaches to chromosomes at the centromere • The centromere is where the sister chromatids are attached Q4 MII

  19. Anaphase II • Centromeres split • Sister chromatids are pulled to opposite poles by the shortening of spindle fibers Q4 AII

  20. Telophase II • Spindle breaks down • Nuclear envelope forms in each of the new cells • Chromosomes decondense Q4 TII

  21. Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Four nonidentical haploid daughter cells Summary of Meiosis II Q2 Entire Overview

  22. Homologous chromosomes in germline cells Homologous pair of replicated chromosomes New combinations of genetic info Synapsis Square Dance

  23. Males and Females are Different! Girls have a “flower” and boys have a “noodle”

  24. vas deferens seminal vesicle bladder urethra prostate bulbourethral gland epididymis testis Male Reproductive System • Gametes are made in the gonads • Sperm are made in the testes • Sperm are made and stored outside of the body • 200-600 million sperm are released with each ejaculation!!! • Trillions of sperm are made in a lifetime

  25. Spermatogenesis Q1 Entire process starts at puberty

  26. uterine tube ovary uterus cervix vagina Female Reproductive System • Gametes are made in the gonads • Oocytes are made in the ovaries • A girl is born with just one million oocytes per ovary • Only 400 eggs will be ovulated between puberty and menopause

  27. Oogenesis Before birth Arrested in Prophase I After puberty (each month) Arrested in Metaphase II Upon fertilization

  28. Polar Bodies • Three polar bodies are generated due to the developing egg hogging all of the cytoplasm • Polar bodies usually degenerate • If fertilized by a sperm, a blighted ovum develops and results in miscarriage

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