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Chapter 10

Meiosis and Sexual Reproduction. Chapter 10. Why Sex. Fig. 10-1b, p.154. Why sex?. Asexual Easier, faster Big population Indentical Bits can make whole indv. No new combos All inherit the same info Clones parthogenesis. Sexual Changing env More variety New combos

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Chapter 10

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  1. Meiosis and Sexual Reproduction Chapter 10

  2. Why Sex Fig. 10-1b, p.154

  3. Why sex? Asexual Easier, faster Big population Indentical Bits can make whole indv. No new combos All inherit the same info Clones parthogenesis Sexual Changing env More variety New combos Involves meiosis (gametes) and fertilization allele

  4. Cost of Sexual Reproduction Fig. 43-2c, p.756

  5. 43.1 (p. 756)Cost of Sexual Reproduction Specialized cells and structures must be formed Special courtship, and parental behaviors can be costly Timing of gamete formation and mating Nurturing developing offspring, either in egg or body, requires resources from mother

  6. 10.2 What Meiosis Does Meiosis – nuclear division that divides parental c-some # by half in specialized reproductive cells Ex: anther, ovules anther ovary

  7. Homologous Chromosomes Carry Different Alleles • Homologous c-some – same shape, length and assortment of genes, line up with each other • Paternal and maternal chromosomes can carry different alleles

  8. Chromosome Number Sum total of chromosomes in a cell Germ cells are diploid (2n) Gametes are haploid (n) Meiosis halves chromosome number

  9. Meiosis: Two Divisions Two consecutive nuclear divisions Meiosis I – aligns with partner Meiosis II – sister chromatids separate DNA is not duplicated between divisions Four haploid nuclei form

  10. 10.4 Factors Contributing to Variation among Offspring Crossing over during prophase I Independent assortment Random alignment of chromosomes at metaphase I Random combination of gametes at fertilization

  11. Crossing Over • Each chromosome becomes zippered to its homologue • All four chromatids are closely aligned • Nonsister chromosomes exchange segments

  12. Effect of Crossing Over After crossing over, each chromosome contains both maternal and paternal segments Creates new allele combinations in offspring

  13. Independent Assortment Microtubules from spindle poles attach to kinetochores of chromosomes randomly, between Prophase I and Metaphase I

  14. Possible Chromosome Combinations As a result of random alignment, the number of possible combinations of chromosomes in a gamete is: 2n (n is number of chromosome types)

  15. Fertilization Which two gametes unite is random Adds to variation among offspring

  16. Life Cycles Plant Animal

  17. Plant Life Cycle sporophyte zygote diploid fertilization meiosis haploid spores gametes gametophytes Fig. 10-8a, p.162

  18. Animal Life Cycle multicelled body zygote diploid fertilization meiosis haploid gametes Fig. 10-8b, p.162

  19. 44.2Spermatogenesis Spermatogonium (2n) divides by mitosis to form primary spermatocyte (2n) Meiosis produces haploid spermatids Spermatids mature to become sperm movie Figure 44.4 Page 775

  20. Male Hormonal Control Hypothalamus GnRH Inhibin Anterior Pituitary FSH LH Leydig Cells Sertoli Cells Testes Testosterone Formation and Development of Sperm

  21. 44.1Oocytes Arrested in Meiosis I Girl is born with primary oocytes already in ovaries Each oocyte has entered meiosis I and stopped Meiosis resumes, one oocyte at a time, with the first menstrual cycle

  22. Ovarian Cycle secondary oocyte first polar body • Follicle grows and matures • Ovulation occurs • Corpus luteum forms antrum corpus luteum primordial follicle Figure 44.8 Page 778

  23. A transparent and somewhat elastic layer, the zona pellucida, starts forming around the primary oocyte. Primary oocyte, not yet released from meiosis I. A cell layer is forming around it. A follicle consists of the cell layer and the oocyte. A fluid-filled cavity (antrum) starts forming in the follicle’s cell layer. Mature follicle. Meiosis I is over. The secondary oocyte and first polar body are now formed. primordial follicle first polar body secondary oocyte The corpus luteum breaks down when the woman doesn’t get pregnant. A corpus luteum forms from remnants of the ruptured follicle. Ovulation. Mature follicle ruptures and releases the secondary oocyte and the first polar body. Fig. 44-8b, p.778

  24. Female Hormonal Control Hypothalamus GnRH Rising estrogen stimulates surge in LH Anterior pituitary Progesterone, estrogens LH FSH Ovary follicle growth, oocyte maturation Estrogen Corpus luteum forms

  25. Mitosis Functions Asexual reproduction Growth, repair Occurs in somatic cells Produces clones Mitosis & Meiosis Compared • Meiosis • Function • Sexual reproduction • Occurs in germ cells • Produces variable offspring

  26. Prophase vs. Prophase I Prophase (Mitosis) Homologous pairs do not interact with each other Prophase I (Meiosis) Homologous pairs become zippered together and crossing over occurs

  27. Anaphase, Anaphase I, and Anaphase II Anaphase I (Meiosis) Homologous chromosomes separate from each other Anaphase/Anaphase II (Mitosis/Meiosis) Sister chromatids of a chromosome separate from each other

  28. Results of Mitosis and Meiosis Mitosis Two diploid cells produced Each identical to parent Meiosis Four haploid cells produced Differ from parent and one another

  29. An Ancestral Connection Was sexual reproduction a giant evolutionary step from aseuxal reproduction? Giardia intestinalis Chlamydomonas Recombination mechanisms are vital for reproduction of euk cells may have evolved from DNA repair mechanisms in prok ancestors

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