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Chromosomes and Meiosis

Chromosomes and Meiosis. Two major types of cells. You have many types of specialized cells in your body, but they can be divided into two major groups: somatic cells germ cells. Somatic Cells. Somatic cells, also called body cells , make up most of your body tissues and organs.

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Chromosomes and Meiosis

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  1. Chromosomes and Meiosis

  2. Two major types of cells • You have many types of specialized cells in your body, but they can be divided into two major groups: • somatic cells • germ cells

  3. Somatic Cells • Somatic cells, also called body cells, make up most of your body tissues and organs. • Your spleen, kidneys, and eyeballs are all made entirely of body cells. • DNA in your body cells is NOT passed on to your children.

  4. Germ Cells • Germ cells are cells in your reproductive organs, the ovaries and testes, that develop into gametes. • Gametes are sex cells- ova, or eggs, in the female, and spermatozoa, or sperm cells, in the male. • Your DNA in your gametes can be passed to your children.

  5. Chromosome Number • Each species has a characteristic number of chromosomes per cell. • This number is not related to the complexity of the animal.

  6. DNA and Chromosomes in Body Cells • Each of your body cells contains a set of 46 chromosomes, which come in two pairs of 23.

  7. Chromosomes • Together, each pair of chromosomes is referred to as a homologous pair. • “Having the same structure.” • Homologous chromosomes are two chromosomes-one inherited from the mother, and one from the father- that have the same length and general appearance. • These chromosomes have copies of the same genes, although the two copies may differ.

  8. Human Chromosomes • Homologous chromosome pairs are assigned a number to each pair of homologous chromosomes, ordered from largest to smallest. • The largest is 1 and the smallest is 23.

  9. Human Chromosomes • Collectively, chromosome pairs 1 through 22 make up your autosomes, chromosomes that contain genes for characteristics not directly related to the sex of an organism. • Chromosome pair 23 is responsible for determining gender.

  10. Chromosomes • Most sexually reproducing species also have sex chromosomes that directly control the development of sexual characteristics. • Humans have two very different sex chromosomes. • X • Y • How sex is determined varies by species.

  11. Sex Chromosomes • In all mammals, an organism’s sex is determine by the XY system: • XX=female • XY=male • Although the X and Y chromosomes pair with each other, they are not homologous.

  12. Sex Chromosomes • X chromosome: • The larger sex chromosome and contains numerous genes, including many that are unrelated to sexual characteristics. • Y chromosome: • A sex chromosome that contains genes that direct the development of the testes and other male traits. It is the smallest chromosomes and carries the fewest genes.

  13. Sexual Reproduction • Sexual reproduction is the fusion of two gametes that result in offspring that are a genetic mixture of both parents. • The actual fusion of an egg and a sperm cell is called fertilization. • When this occurs, the nuclei of the sperm and egg cell fuse to form one nucleus. • The new nucleus must have the correct number of chromosomes for a healthy new organism to develop.

  14. Diploid • Body cells and gametes have different numbers of chromosomes. Your body cells are diploid. What does this mean? • This means that a cell has two copies of each chromosome: one copy from the mother, and one copy from the father. • They can be represented as 2n. • In humans, the diploid chromosome number is 46.

  15. Haploid • Gametes are not diploid cells; they are haploid, represented as n. What does this mean? • Haploid means that a cell has only one copy of each chromosomes. • Each human egg or sperm cell has 22 autosomes and 1 sex chromosome. • In the egg cell, the sex chromosome will always be X. • In the sperm cell, the sex chromosome can be either X or Y.

  16. Haploid (n) • Diploid (2n)

  17. Meiosis • Germ cells in your reproductive organs undergo the process of meiosis to form gametes. • Meiosis is a form of nuclear division that divides a diploid cell into haploid cells. • This process is essential for sexual reproduction.

  18. Meiosis

  19. MEIOSIS DIVISION OF THE SEX CELLS WHY I DON’T LOOK EXACTLY LIKE BOTH OF MY PARENTS

  20. PONDER THIS….. • IF A NEW HUMAN IS CREATED FROM A MOMMY CELL AND A DADDY CELL COMING TOGETHER (EGG & SPERM)….. • HOW DO YOU AVOID DOUBLING YOUR CHROMOSOME NUMBERS?

  21. SPERM & EGG UNITE = + 46 chromosomes 46 chromosomes 92 chromosomes

  22. Meiosis reduces chromosome number and creates genetic diversity. 4 haploid cells made from 1 diploid cell.

  23. Homologous Chromosome: Chromosomes that are similar (NOT identical) • One chromosome from each parent, same length, containing similar alleles (genes). • Sister chromatids: ½ a chromosome. Homologous chromosomes Sister chromatids

  24. Meiosis I - divides Homologous chromosomes: Prophase I Metaphase I Anaphase I Telophase I Meiosis II - divides sister chromatids: Prophase II Metaphase II Anaphase II Telophase II Cells go through 2 rounds of division in Meiosis: Homologous chromosomes are divided in meiosis1. Sister chromatids are divided in meiosis 2. Homologous chromosomes Sister chromatids

  25. Meiosis I

  26. 1. Prophase I • Centrioles move, spindle fibers start to form • Chromosomes condense • Homologous chromosomes begin to pair up and form TETRAD From Mother From Father

  27. 2. Metaphase I • Chromosomes align along the center of the cell (note difference in alignment) • Each side of cell has chromosomes from both parents • Crossing-over occurs

  28. 3. Anaphase I • Paired homologous chromosomes separate from one another • Move towards opposite ends Chromatids remain attached

  29. 4. Telophase I • Spindle fibers fall apart • Cell goes through cytokinesis

  30. MEIOSIS II

  31. 5. Prophase II • Centrioles and centrosomes move to opposite sides • Spindle fibers start to assemble

  32. 6. METAPHASE II • Chromosomes line up along the middle of the cell. (Note: looks like mitosis now but with ½ of the chromosomes).

  33. 7. ANAPHASE II • Sister chromatids pulled apart from each other • Move to opposite ends.

  34. 8. TELOPHASE II • Nuclear Envelope forms • Spindle fibers break • Cytokinesis occurs  4 haploid gametes.

  35. Sperm become motile Really small, basically only contributing DNA to zygote. 4 sperm produced Much larger, contributes organelles, DNA, and cytoplasm, molecular building blocks, nutrients to zygote. 1 egg and 3 polar bodies produced (polar bodies get broken down) Haploid cells develop into mature gametes = GametogenesisGametes differ between male and female

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