MeiosisMeiosis

STS BiologySTS Biology

Unit 4 GeneticsUnit 4 Genetics

Chapter 11Chapter 11

Chromosome NumberChromosome Number Species have characteristic numbers of Species have characteristic numbers of

chromosomeschromosomes Eukaryotic cells have pairs of Eukaryotic cells have pairs of

homologous chromosomeshomologous chromosomes Cells with a Cells with a doubledouble set of chromosomes set of chromosomes

are are diploid (2n)diploid (2n) Cells with Cells with oneone set of chromosomes are set of chromosomes are

haploid (n)haploid (n)

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

Humans Humans bodybody cells cells are diploid (2N)are diploid (2N) 2N = 462N = 46

GametesGametes - sex cells - sex cells Males – spermMales – sperm Females – eggsFemales – eggs

Gametes are Gametes are HAPLOIDHAPLOID N = 23N = 23

Fertilization restores Fertilization restores the diploid state (N + the diploid state (N + N = 2N)N = 2N)

ZygoteZygote - a fertilized egg (2N)

Meiosis…bottom Meiosis…bottom lineline

Process to make haploid Process to make haploid gametesgametes

Chromosome # is cut in Chromosome # is cut in halfhalf 2N 2N N N

Occurs in ovaries & testesOccurs in ovaries & testes TWO cell divisionsTWO cell divisions Increases genetic Increases genetic

variationvariation

Prior to Prior to Meiosis….INTERPHASEMeiosis….INTERPHASE

What happens during Interphase???What happens during Interphase??? DNA REPLICATION!!!DNA REPLICATION!!!

2N

2N