1 / 39

Meiosis

Meiosis. Cell division for the formation of egg cells and sperm cells. Do Now: take 5 minutes to review quietly. Homework: 11-4 worksheets. Mitosis occurs to help organisms grow , heal or for asexual reproduction. It makes more somatic cells.

kinsman
Download Presentation

Meiosis

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Meiosis Cell division for the formation of egg cells and sperm cells

  2. Do Now: take 5 minutes to review quietly Homework: 11-4 worksheets

  3. Mitosis occurs to help organisms grow, heal or for asexual reproduction. It makes more somatic cells. Daughter cells are clones of each other And of the original parent

  4. Somatic cells are the cells that make up your body; they are body cells. Cells in ovaries and testes will become reproductive cells; these are called germ cells.

  5. After Interphase, somatic cells will divide by mitosis; germ cells will divide by meiosis. Somatic cells: Mitosis Germ cells: Meiosis Interphase

  6. Meiosisis a specialized type of cell division that occurs in germ cells and forms egg and sperm cells. Daughter cells are unique to each other And have half the DNAof the original parent

  7. Why must reproductive cells have half the DNA of normal body cells?

  8. Because sperm and egg cells only have one set(half) of the genetic material, they are called haploid (n) cells. In humans, one set of chromosomes consists of 23 chromosomes. The haploid number (n) equals 23.

  9. When a haploid egg cell is joined by a haploid sperm cell, the result is a diploid (2n) cell. This is because it has two complete sets of chromosomes.

  10. Each chromosome from your mother corresponds to a chromosome from your father. Corresponding chromosomes are called homolgous chromosomes.

  11. Karyotype Photograph of chromosomes grouped in order of pairs Meiosis Overview

  12. Interphase Just like before Mitosis, Interphase includes Growth, Protein Synthesis and DNA Replication.

  13. DNA Replication

  14. Tetrads form when homologous chromosomes have paired up in the cell. (4 sister chromatids lined up)

  15. Crossing Over: When segments of chromosomes break off and reattach to homologous chromosomes: exchanges genetic material.

  16. Interphase M e i o s i s I M e i o s i s I I

  17. M e i o s i s I Prophase I Metaphase I Anaphase I Telophase I Meiosis II

  18. M e i o s i s I I Prophase II Metaphase II Anaphase II Telophase II Spermatogenesis

  19. Meiosis Overview: • Start: Diploid germ cell with homologous chromosomes (2n=46) • Replicate DNA: still diploid, now 2 identical copies of DNA • Meiosis I: homologous chromosomes separate, now haploid (n=23), sister chromatids attached • Meiosis II: haploid (n=23), sister chromatids separate

  20. See it in action…

  21. Gamete Formation: Spermatogenesis 1st Meiotic division (haploid) (diploid male germ cell) After DNA Replication (diploid) Finished Sperm cells (haploid) 2nd Meiotic division (haploid)

  22. Gamete Formation:Oogenesis three polar bodies (haploid) first polar body (haploid) (diploid female germ cell) After DNA Replication (diploid) 1st Meiotic Division (haploid) 2nd Meiotic Division (haploid) Genetic Variation

  23. Meiosis increases genetic variation in offspring Factor these in with Crossing Over • Independent assortment • Each gamete you produce contains one of roughly 8 million possible combinations of chromosomes inherited from your mother and father. • Random fertilization • The random fusion of a single sperm with a single ovum during fertilization will produce a zygote with any of about 64 trillion (8 million × 8 million) combinations of chromosomes!

  24. 1 2 3 Two types of gametes Independent assortment: Chromosomes line up during metaphase I independently of each other. …the resulting gametes have a different assortment ofchromosomes

  25. Random fertilization further increases genetic variation

  26. Mitosis and Meiosis work together in the human life cycle

  27. Mitosis vs. Meiosis

  28. Mitosis and Meiosis are two different types of Cell Division • In Mitosis • Cell division makes two clones of the parent cell • For growth, healing and asexual reproduction • Maintains the same number of chromosomes • In Meiosis • Cell division makes four unique daughter cells • With half of the DNA of the parent cell • To make sperm cells and egg cells (gametes) • Reduces the number of chromosomes by half

  29. If Things go Wrong with Meiosis The cause of chromosomal disorders

  30. Karyotype Meiosis Overview

  31. Nondisjunction • Spindles do not attach properly during metaphase, and chromosomes or chromatids do not separate. • Results in too many or not enough chromosomes in gametes

  32. Klinefelter’s Syndrome: XXY Turner’s Syndrome: X Down’s Syndrome: Trisomy 21

  33. Structure Alterations occur because of mistakes in Crossing Over • Deletion When part of the chromosome breaks off • Duplication When part of the chromosome repeats itself • Inversion When two parts of a chromosome flip • Translocation when one part of a chromosome breaks off, then reattaches in the wrong place

  34. Can you identify the chromosomal alterations?

  35. Cri du Chat Syndrome: Deletion from Chromosome 5 Emanuel Syndrome: Translocation of 11 and 22 Chromosome 15q Duplication Syndrome: Diagnosed with Autism

  36. In Conclusion… • Meiosis occurs to form gametes for sexual reproduction • It involves forming 4 haploid daughter cells • Because of Crossing over, Independent Assortment and Random Fertilization, it increases genetic variability • Nondisjunction can result in the incorrect number of chromosomes.

  37. Vocabulary to pay special attention to: • Somatic cells • Gametes • Haploid (n) • Diploid (2n) • Homologous chromosomes • Tetrad • Crossing over

More Related