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Sexual Reproduction

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This detailed overview of meiosis outlines the key processes involved in the formation of gametes, highlighting the essential phases of Meiosis I and II. Meiosis is critical for reducing chromosome numbers by half, resulting in haploid cells that contribute to genetic diversity through mechanisms like crossing over and genetic recombination. This complex process not only forms gametes but also enhances genetic variation in populations. Explore the stages of meiosis, including interphase, prophase, metaphase, anaphase, and telophase, to gain a comprehensive understanding of this vital biological function.

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Sexual Reproduction

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  1. Sexual Reproduction SBI3U Ms. De Sousa

  2. Meiosisallows: 1. The formation of gametes 2. Geneticreduction: reduces the number of chromosomes to half (23) 3. GeneticRecombination: differentcombinations of alleles are formed. Contributes to genetic variation in society

  3. MEIOSIS • Meiosis occurs in somatic diploid cells(cells with 46 chromosomes)and produces 4 gametes, haploid cells. • Unlike mitosis, these gametes do not divide further, but instead fuse with another gamete to make a diploid zygote. (i.e. sperm fuses with the egg) • There are two main phases: Meiosis I and Meiosis II

  4. Begins as a diploidcell (2n) and becomes a haploidclel) Meiosisissubdividedinto 2 main phases: Meiosis I, Meiosis II

  5. Phases of meiosis • Meiosi I: Involves the separation of homologous chromosomes intotwo new daughtercells. • Meiosis II: Involves the seeparation of sisterchromatidsinto 4 new daughtercells. (Each of the previousdaughtercellsseparateinto 2)

  6. Stage 1: Interphase • The cellgoesthrough the G1, S and G2 stages. (similarly to Mitosis) • DNA replicates and is in the form of chromatin • Centrosomereplicates (2 centrosomes) • The cellisdiploid(46 chromosomes)

  7. Meiosis i Stage 1: Prophase I • Nuclearenvelopedisapears and chromatincondenses and becomes chromosomes • Homologous chromosomes pair (tetrads) • Synapsisoccurs, a proteinholdshomologous chromosomes together • Crossing Over, non sisterchromatids exchange genetic information. • Centrosomes move to the poles and spindlefibersform

  8. Crossing over Nonsisterchromatids Eachgene of one homologue isalignedwith the other homologue The non sisterchromatids – one maternal and one paternalchromatid of a homologous pair – are brokenat the same place thenrejoined to eachothers DNA Genetic information isexchanged

  9. Meiosis i Stage 2: Metaphase I • Homologous chromosomes (tetrads) line up on the metaphase plate of the cell • One chromosome of each pair isfacingeach pole • Spindlefibersattach to each homologue at the centromere

  10. Meiosis i Stage 3: Anaphase I • Homologous chromosomes (tetrads) separate and go to opposite poles • Cenromeresstay in tact because the sisterchromatids do not separate • Chromosome numberisnowhaploid (n)

  11. Meiosis i Stage 4: Telophase I • Homologous chromosomes uncoil (formingchromatin) • Spindlefibersdisappear • Nuclear membrane formsaroundeachnuclei • Cytokenesisoccurssimultaneously • Formation of haploiddaughtercells(eachwith 23 chromosomes)

  12. Meiosis II

  13. Meiosis ii Stage 6: Prophase II • Nuclear enveloppe disappears • Spindleapparatusforms

  14. Meiosis ii Stage 7: Metaphase II • Chromosomes are positioned on metaphase plate • Due to crossing over in meiosis I, the sisterchromatids are no longer identical • The spindlefibersare attached to the centromeres

  15. Meiosis ii Stage 8: Anaphase II • The centromere of each chromosome separates • Sisterchromatids come apart • Individual chromosomes move to opposite poles of the cell

  16. Meiosis ii Stage 9: Telophase II • Chromosomes decondenseintochromatin • Nucleiforms • Cytokenesisoccurssimultaneouslyamdseparates the cytoplasm and formstwo new haploiddaughtercells

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