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Meiosis

Meiosis. Terminology. Homologous chromosome: 2 chromosomes that make up a matched pair in a diploid cell Diploid cell: contains 2 sets of chromosomes (2n cell) Haploid cell: contains a single set of chromosomes (n cell). Males vs Females.

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Meiosis

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  1. Meiosis

  2. Terminology • Homologous chromosome: 2 chromosomes that make up a matched pair in a diploid cell • Diploid cell: contains 2 sets of chromosomes (2n cell) • Haploid cell: contains a single set of chromosomes (n cell)

  3. Males vs Females • Females: 23 homologous pairs, basically identical chromosomes • Males: all but one pair are homologous • Sex chromosomes are different: • Female= XX • Male= XY

  4. Sex Chromosome vs Autosome • Sex chromosome: determines a person’s sex (male or female) • Autosome: Chromosome not directly involved in determining an individual’s sex

  5. Humans • Somatic cells (body cells) are 2n • Gametes (egg and sperm cells) are n • 23 chromosomes (22 autosomes and 1 sex chromsome) • Made by meiosis • Why would gametes only have 23 chromosomes?

  6. Meiosis • 2 divisions • Meiosis I • Meiosis II • Halves the chromosome number • Exchanges genetic info between homologous chromosomes

  7. Prophase I • Homologous chromosomes stick together in pairs • Result is called tetrad (4 chromatids stuck together) • Spindle Forms • “Crossing over” occurs • Rearranges genetic information

  8. Metaphase I • Tetrads align in the middle of the cell

  9. Anaphase I • Chromosomes move towards opposite poles • Move as a pair

  10. Telophase I and Cytokinesis • Chromosomes arrive at the poles • Each pole has a haploid chromosome set • Two haploid daughter cells are formed • Chromosomes DO NOT duplicate again

  11. Meiosis II • Essentially the same as mitosis • Prophase II: Spindle forms, Chromosomes move towards center of cell • Metaphase II: Chromosomes are aligned at middle of cell • Anaphase II: Sister chromatids separate • Telophase II: Nuclei form at cell poles, cytokinesis takes place

  12. Result of Meiosis • 4 haploid daughter cells • Contain single chromosomes • Genetically Unique

  13. Comparison 1 1 1 2 2 4 46 (2n) 23 (n) Individually By homologous pair Genetically Identical Genetically Unique Repair, growth, development Gamete formation

  14. POP QUIZ • How many cells are produced in meiosis? • Are they genetically identical? • Why do gametes only have 23 chromosomes? • Are males XX or XY? • What are the 4 stages of mitosis?

  15. Answers • 4 cells • No, they are not genetically identical • 23 chromosomes come from mom and 23 chromosomes come from dad • XY • PMAT

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