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Meiosis & Sexual Reproduction

Meiosis & Sexual Reproduction. Sexual Reproduction. Involves: Meiosis Gamete production Fertilization Produces genetic variation among offspring. Sexual Reproduction Shuffles Alleles. offspring inherit new combinations of alleles, leading to variations in traits

charity-herrera
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Meiosis & Sexual Reproduction

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  1. Meiosis & Sexual Reproduction

  2. Sexual Reproduction • Involves: Meiosis Gamete production Fertilization • Produces genetic variation among offspring

  3. Sexual Reproduction Shuffles Alleles • offspring inherit new combinations of alleles, leading to variations in traits • variation in traits is the basis for evolutionary change

  4. Variation • Sexual reproduction results in greater variation among offspring than does asexual reproduction. • Two parents give rise to offspring that have unique combinations of genes. • Offspring vary genetically from their siblings and from both parents

  5. Meiosis • function: production of gametes • where: gonads of the mature adult; ovaries & testes. • two consecutive nuclear divisions (Meiosis I & Meiosis II) • DNA is NOT replicated during interkinesis • result: 4 haploid (1n) daughter cells

  6. Meiosis reduces the chromosome number from diploid to haploid. Meiosis, like mitosis, is preceded by chromosome duplication… …but, in meiosis the cell divides twice to form four daughter cells.

  7. Meiosis I • starts with synapsis, the pairing of homologous chromosomes • crossing over homologous chromosomes exchange corresponding segments. • each homologous pair separates producing two daughter cells, each with one set of chromosomes

  8. Prophase I Metaphase I Anaphase I Telophase I Meiosis I - Stages

  9. MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Sister chromatids remain attached Microtubulesattached to kinetochore Centrosomes (with centriole pairs) Metaphaseplate Sites of crossing over Spindle Centromere(with kinetochore) Homologouschromosomes separate Sisterchromatids Nuclearenvelope Tetrad Chromatin • The stages of meiosis Figure 8.14 (Part 1)

  10. What are homologous chromosomes? • Each chromosome can be distinguished by its size, position of the centromere, and by pattern of staining with dyes. • Homologous chromosomes carry genes that control the same traits.

  11. Homologous Chromosomes

  12. TEM 2,200 Tetrad Crossing over increases genetic variability. Genetic recombination results from crossing over during prophase I of meiosis and increases variation still further.

  13. MEIOSIS II: Sister chromatids separate TELOPHASE IAND CYTOKINESIS TELOPHASE IIAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavagefurrow Sister chromatidsseparate Haploid daughter cellsforming Figure 8.14 (Part 2)

  14. Prophase II Metaphase II Anaphase II Telophase II Meiosis II - Stages

  15. Fertilization is the union of two haploid gametes; one from each parent. Ex: in humans the egg and sperm each contain 23 chromosomes so after fertilization a zygote will have 46 chromosomes.

  16. Fertilization/Zygote

  17. Early Embryological Development

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