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Chromosomes and Meiosis Unit

Explore the differences between somatic cells (diploid) and gametes (haploid), as well as the comparative sizes of diploid and haploid cells. Learn about chromosome numbers in various living things and understand the types of chromosomes. Discover the differences between homologous chromosomes and sister chromatids, and the processes of meiosis and gametogenesis. Compare mitosis and meiosis in terms of genetic diversity and cell types.

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Chromosomes and Meiosis Unit

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  1. Chromosomes and Meiosis Unit

  2. Cell Types 1) Somatic Cells (aka: body cells) - are diploid (2n) - DNA not passed on

  3. Cell Types 2) Gametes (aka: sex cells) - ex: ova (egg) and spermatozoa (sperm) - are haploid (1n) - DNA passed on

  4. Egg and Sperm Comparative Size

  5. Diploid vs. Haploid Diploid cells have two copies of each chromosome: one copy from the mother and one from the father. Haploid cells have only one copy of each chromosome

  6. Look at the following chromosome numbers of these living things. Do you notice anything about the numbers?

  7. Chromosome Numbers of Various Living Things

  8. Chromosomes Each species has a characteristic number of chromosomes

  9. That fact prevents this from happening Nothing =

  10. That fact allows this to happen + Pug Beagle

  11. That fact allows this to happen = Puggle

  12. That fact allows this to happen Mule = male donkey and a female horse

  13. That fact allows this to happen Liger Tigon

  14. Chromosomes (cont) Types 1) Autosomes 2) Sex Chromosomes - female = XX male = XY

  15. The sex of some species is determined by the temperature of the environment during incubation (mostly occurs in reptiles)

  16. Chromosomes (cont) Humans have 46 chromosomes (23 pairs) - 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair) - a diploid # (2n) of 46 and a haploid # (1n) of 23

  17. Karyotype = picture of an individual’s chromosomes

  18. Homologous Chromosomes vs. Sister Chromatids Homologous Chromosomes = two separate chromosomes, one from mom and one from dad - very similar in size and carry the same genes, but they are not copies of one another

  19. Homologous Chromosomes vs. Sister Chromatids (cont) In contrast, each half of a duplicated chromosome is called a chromatid - together, the two chromatids are called sister chromatids - thus, sister chromatids refers to the duplicated chromosome that remain attached (by the centromere)

  20. Homologous chromosomes (shown duplicated) are two separate chromosomes – one inherited from the mother and one from the father Homologous Chromosomes Sister Chromatids Sister Chromatids

  21. Homologous Chromosomes vs. Sister Chromatids (cont) Homologous chromosomes split in Meiosis I Sister chromatids split in Meiosis II

  22. Meiosis = a form of nuclear division that divides a diploid cell into a haploid cell - makes egg and sperm - 2 rounds of division (Meiosis I and Meiosis II)

  23. Meiosis (cont) Meiosis I – divides homologous chromosomes Meiosis II – divides sister chromatids The overall process produces haploid cells.

  24. Meiosis I

  25. Meiosis II

  26. Gametogenesis 1) spermatogenesis = sperm production (4 haploid cells) - even distribution

  27. Spermatogenesis

  28. Gametogenesis (cont) 2) oogenesis = egg production (1 haploid cell) - uneven distribution (polar bodies created)

  29. Oogenesis

  30. Mitosis - Produces genetically identical cells - Results in diploid cells - Takes place throughout an organism’s life - Involved in asexual reproduction Meiosis - Produces genetically unique cells - Results in haploid cells - Takes place only at certain time in life cycle - Involved in sexual reproduction Comparing Mitosis and Meiosis

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