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Understanding Meiosis: The Role of Chromosomes in Sexual Reproduction

Dive into the intricate process of meiosis, where chromosome numbers are halved to produce haploid cells essential for sexual reproduction. This process includes stages such as Prophase I, where homologous chromosomes undergo synapsis and crossing over, resulting in genetic variation. Discover the key differences between meiosis and mitosis, the significance of crossing over, and how fertilization restores the diploid chromosome number. Explore thought-provoking questions about genetic diversity and the mechanisms that ensure hereditary characteristics in offspring.

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Understanding Meiosis: The Role of Chromosomes in Sexual Reproduction

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Presentation Transcript

  1. Reebop Wrap-up • What happens to the chromosome number during meiosis? What types of cells are made? • Explain how the diploid number of chromosomes is restored.

  2. What are some differences between sexual and asexual reproduction?

  3. Meiosis and Sexual Reproduction

  4. Focus Questions: Things to ponder during the investigation • EQ: How does Meiosis compare to Mitosis? What is the same or different? • EQ: How and when during meiosis are chromosomes reduced to half the number present in the parent cell? • EQ: What two events during Meiosis provide an increased chance for genetic variation or new heritable characteristics in offspring?

  5. Meiosis • Interphase is the same. Replication still occurs during S stage. • Cells alive Goes through PMAT twice.

  6. Prophase I • Synapsis occurs: Replicated Homologous chromosomes find each other and pair up. • Crossing over occurs: Exchange of genetic material between homologues.

  7. Karyotypes

  8. Metaphase I • Homologues line up side by side. (two rows of 23 chromosomes) • 50:50 chance of maternal or paternal chromosomes aligning on either side.

  9. Anaphase I • Homologous pairs separate and are pulled to opposite sides. • One set of chromosomes is pulled to each side. (haploid)

  10. Meiosis II: (PMAT II) • Meiosis II is the same as Mitosis. • Two haploid cells repeat PMAT and Cytokinesis. • Four haploid cells each containing 23 chromosomes are produced. • http://www.lewport.wnyric.org/jwanamaker/animations.htm

  11. Life After Fertilization • Mitosis and differentiation of cells takes over to produce an embryo.

  12. Why is Meiosis Important? • Crossing over results in genetic recombination and creates genetic variation within a population. • Food for thought: • There are 70,368,744,000,000 chromosomal combinations possible without crossing over. • If crossing over occurs once, then 4,951,760,200,000,000,000,000,000,000 combinations of genetically different zygotes are possible for one couple.

  13. Form of Asexual reproduction One division Conserves diploid number Occurs everywhere to produces more somatic cells Produces two identical daughter cells (diploid) Chromosomes line up end to end during metaphase Sexual reproduction Two divisions Reduction division (diploid  haploid) Occurs in gonads to produce gametes Produces four haploid cells Homologues pair in prophase I Crossing over occurs during prophase I Chromosomes line up side by side during metaphase I and then end to end in metaphase II Mitosis vs. Meiosis

  14. Focus Questions • How does meiosis maintain a constant number of chromosomes in the body cells of organisms that reproduce sexually? 2. How does fertilization restore the diploid number of chromosomes in humans? 3. How does crossing over in meiosis result in genetic variation?

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