Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Meiosis for moodle


Published on

Published in: Technology
  • Dating direct: ❤❤❤ ❤❤❤
    Are you sure you want to  Yes  No
    Your message goes here
  • Follow the link, new dating source: ❤❤❤ ❤❤❤
    Are you sure you want to  Yes  No
    Your message goes here

Meiosis for moodle

  1. 1. Meiosis STS Biology Unit 4 Genetics Chapter 11
  2. 2. Chromosome Number
  3. 3. Chromosome Number <ul><li>Eukaryotic cells have pairs of homologous chromosomes </li></ul><ul><li>Cells with a double set of chromosomes are diploid (2n) </li></ul><ul><li>Cells with one set of chromosomes are haploid (n) </li></ul>
  4. 4. <ul><li>Humans body cells are diploid (2N) </li></ul><ul><ul><li>2N = 46 </li></ul></ul><ul><li>Gametes - sex cells </li></ul><ul><ul><li>Males – sperm </li></ul></ul><ul><ul><li>Females – eggs </li></ul></ul><ul><li>Gametes are HAPLOID </li></ul><ul><ul><li>N = 23 </li></ul></ul><ul><li>Fertilization restores the diploid state (N + N = 2N) </li></ul><ul><li>Zygote - a fertilized egg (2N) </li></ul>
  5. 5. Meiosis…bottom line <ul><li>Process to make haploid gametes </li></ul><ul><li>Chromosome # is cut in half </li></ul><ul><ul><li>2N  N </li></ul></ul><ul><li>Occurs in ovaries & testes </li></ul><ul><li>TWO cell divisions </li></ul><ul><li>Increases genetic variation </li></ul>
  6. 6. Prior to Meiosis….INTERPHASE <ul><li>What happens during Interphase??? </li></ul><ul><ul><li>DNA REPLICATION!!! </li></ul></ul>2N 2N
  7. 7. Meiosis I <ul><li>Prophase I – homologous chromosomes form tetrads & crossing over occurs </li></ul><ul><li>Metaphase I – tetrads line up along the middle </li></ul><ul><li>Anaphase I – homologous chromosomes separate </li></ul><ul><li>Telophase I – two nuclei form </li></ul><ul><li>Cytokinesis I – cells separate </li></ul>2N N N
  8. 8. Crossing Over <ul><li>Occurs in Prophase I </li></ul><ul><li>Chromosomes exchange portions of their chromatids </li></ul><ul><li>Increases genetic variation </li></ul>
  9. 9. Meiosis II <ul><li>Prophase II – spindle forms, prepares for division </li></ul><ul><li>DNA replication DOES NOT occur between Meiosis I & II </li></ul><ul><li>Metaphase II – chromosomes align along the center </li></ul><ul><li>Anaphase II – sister chromatids separate </li></ul><ul><li>Telophase II – nuclei reform; cytokinesis </li></ul>N N N N N N Looks A LOT like MITOSIS!
  10. 10. Meiosis in Men vs. Women <ul><li>Men: 4 sperm are made </li></ul><ul><li>Women: only 1 egg is made </li></ul>
  11. 11. Meiosis vs. Mitosis
  12. 12. Independent Assortment <ul><li>Mendel’s Law of Independent Assortment </li></ul><ul><li>Alleles (form of a gene) separate independently of each other </li></ul><ul><li>Leads to the formation of MANY different gametes </li></ul>
  13. 13. Meiosis Summary <ul><li>Chromosome number is cut in half! </li></ul><ul><li>Produces haploid gamete cells – egg and sperm </li></ul><ul><li>Tetrads form during Prophase I </li></ul><ul><ul><li>Crossing over occurs in tetrad formation – leads to increased genetic variation </li></ul></ul><ul><li>Two cell divisions, but DNA does not replicate between divisions </li></ul><ul><li>Results in 4 sperm cells in men and 1 egg in women </li></ul><ul><li>Which chromosomes wind up in which sex cells? It’s random…due to independent assortment!! </li></ul>