1. MeiosisMeiosis
STS BiologySTS Biology
Unit 4 GeneticsUnit 4 Genetics
Chapter 11Chapter 11

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. Chromosome Number (cont.)Chromosome Number (cont.)

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. 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. Prior to Meiosis….INTERPHASEPrior to Meiosis….INTERPHASE
 What happens during Interphase???What happens during Interphase???
 DNA REPLICATION!!!DNA REPLICATION!!!
2N
2N

7. Prior to Meiosis….INTERPHASEPrior to Meiosis….INTERPHASE
 What happens during Interphase???What happens during Interphase???
 DNA REPLICATION!!!DNA REPLICATION!!!
2N
2N