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Meiosis

Meiosis. Pgs. 96-100. Sexual Reproduction and Genetics. Meiosis - General Overview. Human body cells have 46 chromosomes. Each parent contributes 23 chromosomes. Takes place in sex cells (gametes): egg and sperm One cell becomes 4 NON-IDENTICLE cells. Sexual Reproduction and Genetics.

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Meiosis

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  1. Meiosis • Pgs. 96-100

  2. Sexual Reproduction and Genetics Meiosis - General Overview • Human body cells have 46 chromosomes • Each parent contributes 23 chromosomes • Takes place in sex cells (gametes): egg and sperm • One cell becomes 4 NON-IDENTICLE cells

  3. Sexual Reproduction and Genetics Meiosis – Homologous Chromosomes Chromosomes and Chromosome Number • Same length • Same centromere position • Carry genes that control the same inherited traits • One is from mother, one is from father = a matching set

  4. Sexual Reproduction and Genetics Meiosis Haploid and Diploid Cells • An organism produces gametes to maintain the same number of chromosomes from generation to generation. • Human gametes contain 23 chromosomes. • A cell with n chromosomes is called a haploid cell. • A cell that contains 2n chromosomes is called a diploid cell.

  5. Sexual Reproduction and Genetics • When gametes combine in fertilization, the number of chromosomes is restored. Meiosis Meiosis I • The sexual life cycle in animals involves meiosis. • Meiosis produces gametes.

  6. Sexual Reproduction and Genetics Meiosis Meiosis I • Interphase • Chromosomes replicate. • Chromatin condenses. Interphase

  7. Sexual Reproduction and Genetics Meiosis Meiosis I • Prophase I • Pairing of homologous chromosomes occurs. • Each chromosome consists of two chromatids. Prophase I • The nuclear membrane breaks down. • Spindles form.

  8. Sexual Reproduction and Genetics Meiosis Meiosis I • Prophase I • Crossing over produces exchange of genetic information. • Crossing over—chromosomal segments are exchanged between a pair of homologous chromosomes.

  9. Sexual Reproduction and Genetics Meiosis Meiosis I • Metaphase I • Chromosome centromeres attach to spindle fibers. Metaphase I • Homologous chromosomes line up at the equator.

  10. Sexual Reproduction and Genetics • Homologous chromosomes separate and move to opposite poles of the cell. Meiosis Meiosis I • Anaphase I Anaphase I

  11. Sexual Reproduction and Genetics Meiosis Meiosis I • Telophase I • The spindles break down. Telophase I • Chromosomes uncoil and form two nuclei. • The cell divides.

  12. Sexual Reproduction and Genetics • A second set of phases begins as the spindle apparatus forms and the chromosomes condense. Meiosis Meiosis II • Prophase II Prophase II

  13. Sexual Reproduction and Genetics • A haploid number of chromosomes line up at the equator. Meiosis Meiosis II • Metaphase II Metaphase II

  14. Sexual Reproduction and Genetics • The sister chromatids are pulled apart at the centromere by spindle fibers and move toward the opposite poles of the cell. Meiosis Meiosis II • Anaphase II Anaphase II

  15. Sexual Reproduction and Genetics • The chromosomes reach the poles, and the nuclear membrane and nuclei reform. Meiosis Meiosis II • Telophase II Telophase II

  16. Sexual Reproduction and Genetics Meiosis Meiosis II • Cytokinesis results in four haploid cells, each with n number of chromosomes. Cytokinesis

  17. Sexual Reproduction and Genetics Meiosis The Importance of Meiosis • Meiosis consists of two sets of divisions • Produces four haploid daughter cells that are not identical • Results in genetic variation

  18. Sexual Reproduction and Genetics Meiosis Meiosis Provides Variation • Depending on how the chromosomes line up at the equator, four gametes with four different combinations of chromosomes can result. • Genetic variation also is produced during crossing over and during fertilization, when gametes randomly combine.

  19. Mitosis vs Meiosis

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