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Asexual Reproduction

Asexual Reproduction. Sexual Reproduction. Requires a male and a female Requires a sperm and an egg cell Offspring are not identical to each other or their parents. How do offspring and parents compare when using asexual reproduction?. Meiosis.

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Asexual Reproduction

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  1. Asexual Reproduction

  2. Sexual Reproduction • Requires a male and a female • Requires a sperm and an egg cell • Offspring are not identical to each other or their parents. • How do offspring and parents compare when using asexual reproduction?

  3. Meiosis Cell division that results in the production of the sperm or egg Also known as Reduction Division

  4. Meiosis • Occurs in the gonads (ovaries and testes) • Results in gametes (sperm and eggs) • Results in Haploid (monoploid) cells-cells that have half the normal number of chromosomes found in body cells

  5. Meiosis • The sperm and egg that form from meiosis are haploid (1N) • When the sperm fertilizes the egg, the zygote that forms is diploid (2N) • All body cells arise from the zygote by Mitosis, therefore body cells are diploid

  6. Meiosis • Meiosis involves two successive divisions which will result in four new haploid cells • The two division are known as Meiosis 1 and Meiosis 2 - both have prophase, metaphase, anaphase and telophase

  7. Prophase 1 • Each wound up DNA is double stranded • Each side is called a Chromatid • The two chromatids are held together by a Centromere

  8. Homologous Chromosomes have the same size and shape

  9. A B PROPHASE 1 • Information on the chromosomes are called genes • Each gene controls for one trait • There are many genes on one chromosome • Genes on the same chromosome are called LINKED

  10. PROPHASE 1 • During Prophase I the Homologous chromosomes pair up (synapsis) to form a bivalent or tetrad structures. • Synapsis brings the homologous chromosomes side by side and intertwines the chromatids

  11. A B a b PROPHASE 1 • Parts of one chromosome may break off and switch places with the other

  12. a B PROPHASE 1 • Crossing -over will result in new gene combinations A b

  13. 1. What happens during crossing over? Some genetic material is exchanged between two chromatids of homologous chromosomes.

  14. 2. How are the resulting gametes affected by crossing over? The chromosomes of some gametes are recombinant, meaning that they have a combination of genetic material that differs from the diploid cell’s chromosomes.

  15. METAPHASE 1 • During Metaphase I the chromosmes will be pulled by the spindle to line along the equator • The chromosomes line up double file in homologous pairs

  16. ANAPHASE 1 • Homologous Pairs of chromosomes get pulled apart (Segregation) • The chromosomes remain double stranded

  17. TELOPHASE 1 • The cytoplasm divides (cytokenesis) • Each new cell has only half the number of the original chromosomes (reduction division)

  18. INTERKINESIS • Resting Stage

  19. Meiosis 1 Animation

  20. PROPHASE 2 • Prophase 2 is similar to Prophase 1 except that there are now 2 cells with half the number of chromosomes

  21. METAPHASE 2 • the chromosomes line up along the equator single file

  22. ANAPHASE 2 • The centromeres have uncoupled • The spindles pull the chromatids apart • The chromosomes are now single stranded

  23. TELOPHASE 2 • The cytoplasm splits leaving four cells with half the number of chromosomes

  24. Meiosis 2 Animation

  25. Link to Demo

  26. Link to Quiz

  27. 1. What is the result of meiosis I? two non-identical haploid daughter cells

  28. 2. How does the movement of chromosomes in meiosis I differ from that in mitosis? In meiosis I, homologous chromosomes are separated from each other. In mitosis, sister chromatids are separated from each other.

  29. 1. What is the result of meiosis II? four non-identical haploid daughter cells

  30. 2. How are the cells at the start of prophase II different from those at the end of meiosis II? The cells in prophase II have duplicate copies of their chromatids (double stranded). The final cells have single copies.

  31. Sexual Recombination • Creates a greater diversity of individuals in the next generation • It involves three major processes • Crossing Over • Independent Assortment • Gametic Assortment

  32. Independent Assortment • New cells are not identical to each other • Each cell has different combinations of chromosomes in them - one from each homologous pair of chromosomes • There are >8 million chromosome combinations to make each sperm or egg cell

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