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  1. 1. Meiosis Section 10.1 (pp. 270-276)
  2. 2. Terms to Know <ul><li>Genes – a segment of DNA that controls for the production of one protein </li></ul><ul><li>Chromosomes – DNA that becomes tightly coiled before cell divides; one chromosome contains a thousand or more genes </li></ul>
  3. 3. Homologous Chromosomes <ul><li>Homologous Chromosomes-chromosomes that make up a pair, one from each parent. </li></ul><ul><li>A parent will randomly give one copy of their chromosome to their offspring </li></ul><ul><li>They are the same length and have the same centromere position. They carry genes that control the same traits. </li></ul>
  4. 4. Homologous Chromosomes
  5. 5. Haploid Cell <ul><li>Haploid cell – a cell that contains a haploid, or n, number of chromosomes </li></ul><ul><li>Has one of each kind of chromosome </li></ul><ul><li>Gametes- haploid cell that contain half the chromosomes. </li></ul><ul><li>(Ex: Sex Cells = 23 chromosomes) </li></ul>
  6. 6. Diploid Number <ul><li>Diploid cell – a cell that contains a diploid, or 2 n, number of chromosomes </li></ul><ul><li>One chromosome in each pair comes from the male parent and the other from the female parent. </li></ul><ul><li>Fertilization- process which one haploid gamete combines with another haploid gamete, creating a diploid cell </li></ul>
  7. 7. Chromosome Number <ul><li>Each species of organism contains a characteristic number of chromosomes </li></ul><ul><li>The chromosome number of a species is not related to the complexity of the organism </li></ul>Organism Body cell (2n) Gamete (n) Fruit fly 8 4 Garden pea 14 7 Corn 20 10 Tomato 24 12 Leopard frog 26 13 Apple 34 17 Human 46 23 Chimpanzee 48 24 Dog 78 39 Adder’s tongue fern 1260 630
  8. 8. Meiosis <ul><li>Meiosis- process which gametes are formed. </li></ul><ul><li>Meiosis is cell division that halves the number of chromosomes. The gametes come together in fertilization so the new cell has the correct number of chromosomes </li></ul>
  9. 9. Meiosis <ul><li>Consists of two separate divisions </li></ul><ul><ul><li>Meiosis I </li></ul></ul><ul><ul><li>Meiosis II </li></ul></ul><ul><li>Meiosis I begins with 1 diploid (2n) cell </li></ul><ul><li>By the end of meiosis II there are four haploid (n) cells </li></ul>
  10. 10. Sexual Reproduction <ul><li>Haploid cells are called gametes -sex cells </li></ul><ul><li>Sperm - male gametes ( n ) </li></ul><ul><li>Eggs – female gametes ( n ) </li></ul><ul><li>Zygote – a cell resulting from the fertilization of the egg by a sperm (2 n ) </li></ul><ul><li>The zygote can develop into a multicellular organism by mitosis </li></ul>
  11. 11. Meiosis I
  12. 12. Meiosis Intro Clip
  13. 13. Phases of Meiosis I Interphase Cell replicates its chromosomes Prophase I Replicated chromosomes (sister chromatids) are visible. Tetrad forms (pair of homologous chromosomes) in a process called synapsis. Crossing over may occur Metaphase I Centromeres attach to spindle fibers, tetrad is pulled to equator Anaphase I Homologous chromosomes (2 sister chromatids) separate to opposite ends Telophase I Spindle breaks down, chromosomes uncoil, cytoplasm divides to form 2 new cells (sister chromatids)
  14. 14. Phases of Meiosis II Interphase Short phase, chromosomes do not replicate Prophase II Spindles form in each of 2 new cells Metaphase II Centromeres attach to spindle fibers and pulls sister chromatids to equator Anaphase II Sister chromosomes separate to opposite poles Telophase II Nuclei re-form, spindle breaks down, chromosomes uncoil, cytoplasm divides
  15. 15. Mitosis Vs. Meiosis <ul><li>Mitosis Meiosis </li></ul><ul><li>One division 2 divisions -Meiosis I &II </li></ul><ul><li>DNA replicates DNA replicates only once </li></ul><ul><li>No Synapsis Synapsis occur in Prophase I </li></ul><ul><li>2 identical cells are formed 2 haploid cells are formed </li></ul><ul><li>Daughter cells are identical Daughter cells not identical </li></ul><ul><li>Mitosis occurs in body cells Meiosis occurs reproduction (somatic cells) cells </li></ul>
  16. 16. Genetic Variation <ul><li>Genetic recombination – the reassortment of chromosomes by crossing over or independent segregation of homologous chromosomes </li></ul><ul><li>Is a major source of variation among organisms </li></ul><ul><li>Source of genetic change in species </li></ul>
  17. 17. Crossing Over <ul><li>Late in prophase I, the homologous chromosomes come together to form tetrads. Arms of nonsister chromatids wind around each other and genetic material may be exchanged </li></ul>
  18. 18. Meiosis Clip
  19. 19. How many different kinds of gametes can an organism produce? <ul><li>Pea plant </li></ul><ul><ul><li>7 pair chromosomes </li></ul></ul><ul><ul><li>Each of seven pairs can line up at the equator in two different ways (2 7 ) </li></ul></ul><ul><ul><li>128 different kinds of sperm are possible </li></ul></ul><ul><ul><li>2 7 = 128 </li></ul></ul><ul><ul><li>When fertilization occurs, 128 X 128 or 16,384 different zygotes are possible! </li></ul></ul>
  20. 20. How many different kinds of gametes can an organisms produce? <ul><li>Human </li></ul><ul><ul><li>23 pair chromosomes </li></ul></ul><ul><ul><li>Each of 23 pairs can line up at the equator in two different ways (2 23 ) </li></ul></ul><ul><ul><li>More than 8 million different kinds of sperm are possible </li></ul></ul><ul><ul><li>When fertilization occurs, 2 23 X 2 23, or 70 trillion different zygotes are possible! </li></ul></ul>
  21. 21. Polyploidy (p. 285) <ul><li>Polyploids – organisms with more than the usual number of chromosome sets </li></ul><ul><li>It is rare in animals…causing death </li></ul><ul><li>It occurs in plants. Flowers and fruits of these plants are larger and healthier than normal </li></ul><ul><li>Ex: Tripolid (3n) </li></ul><ul><li>Tetrapolid (4n) </li></ul>
  22. 22. Mistakes (Polyploids) can be beneficial <ul><li>Tetraploid (4n)- coffee </li></ul><ul><li>Triploid (3n)- apples </li></ul><ul><li>Polyploid chrysanthemums (2n,4n,6n,8n,10n) </li></ul><ul><li>Polyploid (6n)- wheat, oats and sugar cane </li></ul><ul><li>Polyploid (8n)- strawberries </li></ul><ul><li>Plant breeders artificially produce polyploid plants using chemicals. </li></ul>