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Meiosis Part 1

Meiosis Part 1 . Reduction Division Production of Gametes Part 1 . Mitosis: Review . What is the purpose of mitosis? To allow cell copy itself completely To grow, repair, and for non sexual organisms to reproduce What are the four phases of mitosis? Prophase Metaphase Anaphase

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Meiosis Part 1

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  1. Meiosis Part 1 Reduction Division Production of Gametes Part 1

  2. Mitosis: Review • What is the purpose of mitosis? • To allow cell copy itself completely • To grow, repair, and for non sexual organisms to reproduce • What are the four phases of mitosis? • Prophase • Metaphase • Anaphase • Telophase

  3. Mitosis: Review • Name the parts of mitosis below

  4. Mitosis: Review • 2n= normal cell • Mitosis forms what type of cells?

  5. Meiosis vocabulary • Diploid – (2n) the normal number of chromosomes (one from mom and one from dad) • Haploid – (n) half the normal number of chromosomes • Somatic cells – normal bodycells – these are diploid (2n) What are some examples of somatic cells? What cells are not somatic? • Gametes – Reproductive cells (egg and sperm) • These are haploid (n)

  6. Meiosis Meiosis: a form of cell divisionthat creates gametes The process halves the number of chromosomes turning diploid cells (2n) into haploid cells (n)

  7. Meiosis 2n n

  8. Chromosome • Chromosome- ____________________ • Chromatid - is one of two identical strands of DNA making up a chromosome • Centromere– holds two chromatids together to make a chromosome

  9. Chromosome- Draw this Chromosome Chromatid Chromatid Centromere

  10. Homologous Chromosomes • Each organism has chromosomes almost identical sets of chromosomes from each parent. (Hence the 2n) • Each set of these are considered Homologous Chromosomes • Homologous Chromosomes are Chromosomes in cell that pair (synapse) during meiosis Chromosome from mom Chromosome from dad

  11. Meiosis • Meiosis has two parts • Meiosis I • Meiosis II

  12. Meiosis I • At the beginning of meiosis I, homologous chromosomes are attached together to form a tetrad • Homologous chromosomes then cross over with each other exchanging genetic information • Tetrads separate during meiosis I and each new cell has only one of the original homologous chromosomes Tetrad

  13. Meiosis 1 has 4 phases: Prophase I, Metaphase I, Anaphase I, Telophase I MEIOSIS I: Homologous chromosomes separate INTERPHASE PROPHASE I METAPHASE I ANAPHASE I Centrosomes(withcentriolepairs) Microtubules attached tokinetochore Metaphaseplate Sister chromatidsremain attached Sites of crossing over Spindle Nuclearenvelope Sisterchromatids Tetrad Centromere(with kinetochore) Homologouschromosomes separate Chromatin Figure 8.14, part 1

  14. Crossing Over • Crossing over- the exchange of corresponding segments between two homologous chromosomes • Happens during meiosis I • Crossing over mixes the genes from the parents increasing variation

  15. Crossing Over Chromosome from mom Chromosome from dad

  16. MEIOSIS I Crossed over chromosomes PROPHASE I METAPHASE I ANAPHASE I END OF INTERPHASE

  17. Meiosis II • Meiosis II is essentially the same as mitosis • sister chromatids of each chromosome separate • result is four haploid daughter cells Do not change this slide until you watch the animation

  18. MEIOSIS METAPHASE II TELOPHASE I PROPHASE II ANAPHASE II TELOPHASE II

  19. Meiosis II has four phases also MEIOSIS II: Sister chromatids separate TELOPHASE IAND CYTOKINESIS TELOPHASE IIAND CYTOKINESIS PROPHASE II METAPHASE II ANAPHASE II Cleavagefurrow Sister chromatidsseparate Haploiddaughter cellsforming Figure 8.14, part 2

  20. MITOSIS MEIOSIS PARENT CELL(before chromosome replication) Site ofcrossing over MEIOSIS I PROPHASE I Tetrad formedby synapsis of homologous chromosomes PROPHASE Chromosomereplication Chromosomereplication Duplicatedchromosome(two sister chromatids) 2n = 4 Chromosomes align at the metaphase plate Tetradsalign at themetaphase plate METAPHASE I METAPHASE ANAPHASE I TELOPHASE I ANAPHASETELOPHASE Sister chromatidsseparate duringanaphase Homologouschromosomesseparateduringanaphase I;sisterchromatids remain together Haploidn = 2 Daughtercells of meiosis I 2n 2n No further chromosomal replication; sister chromatids separate during anaphase II MEIOSIS II Daughter cellsof mitosis n n n n Daughter cells of meiosis II Figure 8.15

  21. Meiosis Part 2 Karyotypes Differences between sperm and eggs Problems that can occur in Meiosis

  22. Karyotype • A diagram which arranges all of a cell’s chromosomes in order from largest to smallest

  23. Spermatogenesis vs Oogenesis • Spermatogenesis- Process that makes sperm. • Produces 4 sperm • Oogenesis – Process that makes eggs • ONLY produces 1 egg cell

  24. SPERMATOGENESIS b OOGENESIS a spermatogonium oogonium primary spermatocyte primary oocyte meiosis l secondary spermatocyte secondary oocyte polar body meiosis ll spermatids polar bodies (will be degraded) egg

  25. Nondisjunction Nondisjunctionin meiosis I • Nondisjunction- when a mistake occurs during meiosis leading to an abnormal about of chromosomes in a gamete Normalmeiosis II Gametes

  26. Fertilization after nondisjunction in the mother results in a zygote with an extra chromosome Eggcell n + 1 Zygote2n + 1 Spermcell n (normal) Figure 8.21C

  27. Connection: An extra copy of chromosome 21 causes Down syndrome • An extra copy of chromosome 21 shown in the karyotype below causes Down syndrome • Also called trisomy 21 Figure 8.20A, B

  28. Sex Determination-TED ED

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