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11/29/10 Class Notes

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11/29/10 Class Notes

  1. 1. MeiosisMeiosis STS BiologySTS Biology Unit 4 GeneticsUnit 4 Genetics Chapter 11Chapter 11
  2. 2. Chromosome NumberChromosome Number  Species have characteristic numbers of chromosomesSpecies have characteristic numbers of chromosomes  Eukaryotic cells have pairs ofEukaryotic cells have pairs of homologoushomologous chromosomeschromosomes  Cells with aCells with a doubledouble set of chromosomes areset of chromosomes are diploid (2n)diploid (2n)  Cells withCells with oneone set of chromosomes areset of chromosomes are haploid (n)haploid (n)
  3. 3. Chromosome Number (cont.)Chromosome Number (cont.)
  4. 4.  HumansHumans bodybody cells arecells are diploid (2N)diploid (2N)  2N = 462N = 46  GametesGametes - sex cells- sex cells  Males – spermMales – sperm  Females – eggsFemales – eggs  Gametes are HAPLOIDGametes are HAPLOID  N = 23N = 23  Fertilization restores theFertilization restores the diploid state (N + N = 2N)diploid state (N + N = 2N)  ZygoteZygote - a fertilized egg (2N)
  5. 5. Meiosis…bottom lineMeiosis…bottom line  Process to make haploid gametesProcess to make haploid gametes  Chromosome # is cut in halfChromosome # is cut in half  2N2N  NN  Occurs in ovaries & testesOccurs in ovaries & testes  TWO cell divisionsTWO cell divisions  Increases genetic variationIncreases genetic variation
  6. 6. Prior to Meiosis….INTERPHASEPrior to Meiosis….INTERPHASE  What happens during Interphase???What happens during Interphase???  DNA REPLICATION!!!DNA REPLICATION!!! 2N 2N
  7. 7. Prior to Meiosis….INTERPHASEPrior to Meiosis….INTERPHASE  What happens during Interphase???What happens during Interphase???  DNA REPLICATION!!!DNA REPLICATION!!! 2N 2N

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