The Birds and the Bees: Meiosis

Chapter 10

Meiosis exists for two major reasons:

• To divide the number of chromosomes

• To create genetic variability

Haploid v. Diploid Cells

• Haploid- (n) number of chromosomes where (n) is the number of sets of chromosomes. Humans have 23 different types of chromosomes.

• Diploid- (2n), or a cell that has two sets of chromosomes

Soooo…..

• Sperm and egg are haploid. They each have only 23 chromosomes.

23 Chromosomes

23 Chromosomes

Zygote

• When the (n) sperms enters the (n) egg, we get 2n= 2n number of chromosomes, or in the case of a human, 2(23)= 46

• The zygote (a fertilized egg) has 46 chromosomes

Steps in Meiosis

IN THE FIRST CELLULAR DIVISION, NO CENTROMERES DIVIDE!!!

SISTER

CHROMATIDS

IN MEIOSIS II, ALL WE HAVE ARE TWO CELLS DOING MITOSIS!

FROM ONE “GERM CELL” WE PRODUCED 4 GENETICALLY DIVERSE GAMETES!