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Chromosomes and Meiosis

Explore the fascinating world of chromosomes and meiosis, and learn about somatic cells, germ cells, homologous chromosomes, sex chromosomes, diploid and haploid cells, and the process of meiosis. Discover how crossing-over and genetic recombination contribute to genetic diversity.

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Chromosomes and Meiosis

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  1. Chromosomes and Meiosis

  2. Somatic Cells • Also called Body Cells • Make up most of your body tissues and organs

  3. Germ Cells • Are cells in your reproductive organs—ovaries and testes that develop into gametes. • Gametes are sex cells -ova or eggs in female -sperm in male

  4. Chromosome

  5. Homologous Chromosomes • “having the same structure” • Two chromosomes—one from father, one from mother that have the same length and general appearance

  6. Chromosomes 1-22 • Autosomes---chromosomes that contdain genes for characteristics not directly related to the sex of an organizme. • What about chromosome pair #23?

  7. Sex Chromosomes

  8. Unsorted Human Chromosomes

  9. Human Male Karyotype

  10. Human Female Karyotype

  11. Diploid & Haploid Cells • Diploid—a cell that has two copies of each chromosome; one from mother, one from father---chromosomes #1-#22 • Haploid—a cell that has only one copy of each chromosome (also called sec cells); gametes are haploid; chromosome #23

  12. First Division of Meiosis • First division of meiosis • Prophase 1: Duplicated chromatin condenses. Each chromosome consists of two, closely associated sister chromatids. Crossing-over can occur during the latter part of this stage. • Metaphase 1: Homologous chromosomes align at the equatorial plate. • Anaphase 1: Homologous pairs separate with sister chromatids remaining together. • Telophase 1: Two daughter cells are formed with each daughter containing only one chromosome of the homologous pair.

  13. Second Division of Meiosis • Second division of meiosis: Gamete formation • Prophase 2: DNA does not replicate. • Metaphase 2: Chromosomes align at the equatorial plate. • Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole. • Telophase 2: Cell division is complete. Four haploid daughter cells are obtained.

  14. Mutations

  15. Crossing Over • Exchange of chromosome segments between homologous chromosomes during prophase 1 of meiosis.

  16. Crossing Over & Recombination

  17. Genetic Linkage • The top diagram shows paternal (blue) and maternal (red) chromosomes aligned in a germ cell, a cell that gives rise to eggs or sperm. Three DNA sequences are shown, labelled A, B and C. The capital letters represent the paternal alleles and the lower case letters represent the maternal alleles. The middle panel shows the physical process of recombination, which involves crossing over of DNA strands between the paired chromosomes. The bottom panel shows what happens when the crossover is resolved. The maternal and paternal alleles are mixed (recombined) and these mixed chromosomes are passed to the sperms or eggs. If A is the disease gene and B and C are genetic markers, recombination is likely to occur much more frequently between A and C than it is between A and B. This allows the disease gene to be mapped relative to the markers B and C.

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