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Starter Question

Starter Question. 1. Take out a 1/2 of sheet of paper and answer the following question. You do NOT have to write the question. You MUST write in complete sentences. Q- Recall ch. 1 with the Characteristics of Life. How is cell division (mitosis) related to one or more of those characteristics?.

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Starter Question

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  1. Starter Question • 1. Take out a 1/2 of sheet of paper and answer the following question. You do NOT have to write the question. You MUST write in complete sentences. • Q- Recall ch. 1 with the Characteristics of Life. How is cell division (mitosis) related to one or more of those characteristics?

  2. Comparing Mitosis and Meiosis • Mitosis • Cells produced by mitosis have the same number of chromosomes and alleles as the original cell. • Mitosis allows an organism to grow and replace cells. • Some organisms reproduce asexually by mitosis.

  3. 11-4 Meiosis • 11-4 Meiosis

  4. Meiosis • Similar in many ways to mitosis - M2 • Several differences however • Involves 2 cell divisions • Results in 4 cells with 1/2 the normal genetic information. • Vocabulary: • Diploid (2N) - Normal amount of genetic material • Haploid (N) - 1/2 the genetic material. • Meiosis results in the formation of haploid cells. • In Humans, these are the Ova (egg) and sperm. • Ova are produced in the ovaries in females • Process is called oogenesis • Sperm are produced in the testes of males. • Process is called spermatogenesis • Meiosis occurs in 2 phases: Meiosis 1 & Meiosis 2

  5. Chromosome Number- In book pg275 • Chromosome Number • All organisms have different numbers of chromosomes. • A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent.

  6. Chromosome Number • These two sets of chromosomes are homologous. • Each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent.

  7. Purpose of Meiosis • the number of chromosomes per cell is cut in half • Homolgous chromosome in a diploid cell segregate (independently)

  8. Phases of Meiosis • Meiosis involves two divisions, meiosis I and meiosis II. • By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells. • Video of Overview of Meiosis

  9. Meiosis I. • Prior to division, amount of DNA doubles

  10. Phases of Meiosis • MEIOSIS I • ProphaseI • Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. • There are 4 chromatids in a tetrad.

  11. Crossing Over • Segments of homologous chromosomes break and reform at similar locations. • Results in new genetic combinations of offspring. • This is the main advantage of sexual reproduction

  12. Metaphase 1 • During metaphase 1 homologous chromosomes line-up along the metaphase plate • Areas of homologous chromosomes connect at areas called chiasmata

  13. Anaphase 1 • During anaphase 1, each homologous chromosome is pulled to opposite sides of the cell. Unlike mitosis, THE CENTROMERES DO NOT BREAK. • Nuclei may or may not reform following division. • Cytokenesis may or may not occur.

  14. M1- Telophase & Cytokinisis

  15. Phases of Meiosis so far • Meiosis II Meiosis II Telophase I and Cytokinesis I Metaphase II Anaphase II Telophase II and Cytokinesis Prophase II

  16. Meiosis II • Same steps as MITOSIS • DNA does not double • Chromosomes randomly line-up along metaphase plate like regular mitosis. • During anaphase 2, CENTROMERES BREAK and each chromosome is pulled to opposite sides of the cell. • Nuclei reform and cytokenesis usually occurs (although it is often unequal).

  17. Overview of Meiosis

  18. Comparing Mitosis and Meiosis • Meiosis • Cells produced by meiosis have half the number of chromosomes as the parent cell. • These cells are genetically different from the diploid cell and from each other. • Meiosis is how sexually reproducing organisms produce gametes.

  19. Gamete Formation • Gamete Formation • In male animals, meiosis results in four equal-sized gametes called sperm.

  20. Gamete Formation • In female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction.

  21. 11-4 • If the body cells of humans contain 46 chromosomes, a single sperm cell should have • 46 chromosomes. • 23 chromosomes. • 92 chromosomes. • between 23 and 46 chromosomes.

  22. 11-4 • During meiosis, the number of chromosomes per cell is cut in half through the separation of • daughter cells. • homologous chromosomes. • gametes. • chromatids.

  23. 11-4 • The formation of a tetrad occurs during • anaphase I. • metaphase II. • prophase I. • prophase II.

  24. 11-4 • In many female animals, meiosis results in the production of • only 1 egg. • 1 egg and 3 polar bodies. • 4 eggs. • 1 egg and 2 polar bodies.

  25. 11-4 • Compared to egg cells formed during meiosis, daughter cells formed during mitosis are • genetically different, while eggs are genetically identical. • genetically different, just as egg cells are. • genetically identical, just as egg cells are. • genetically identical, while egg cells are genetically different.

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