Meiosis

Sexual Reproduction

Why is meiosis important?

• Make eggs and sperm for reproduction• Genetic diversity – half DNA from father and

half from mother= new combination

• Somatic cells – (any cell other than egg or sperm)-formed from mitosis only -– Have 46 chromosomes and divide to make

identical cells with 46 chromosomes– Diploid (2n)

• Gametes (egg and sperm) – formed from meiosis only– Have 23 chromosomes– Haploid (n)

• Autosomes are the 22 pairs (44) of chromosomes that are not involved in determining gender

• Sex chromosomes are the pair (2) that determine gender

• Homologous chromosomes- pair of chromosomes that are similar in size, shape, and genetic content- one in each pair comes from the father and the other from the mother.

• Humans have ____pairs of homologous chromosomes.

Chromosome Numbers in Cells• Diploid (2n) cell contains 2 sets of

chromosomes (somatic cell)• Haploid (n) cell contains 1 set of chromosome

(gamete)• What happens when 2 haploid cells fuse in

fertilization?

Homologous Chromosomes and Sister chromatids

Mitosis vs Meiosis

• Mitosis – used for Growth– Two daughter cells– genetically identical to parent cell– two full sets of chromosomes (diploid)– makes bigger organism

• Meiosis – used for Reproduction– Four daughter cells– genetically different from parent cell (and each other)– one full sets of chromosomes (haploid)– helps makes another organism (sexual reproduction)

Meiosis- two cell divisionsMeiosis preceded by an interphase (just like mitosis) – chromosomes replicated during the S phase.

Meiosis 1

Stages of Meiosis

Crossing Over

Crossing Over in ActionWhat is the advantage of crossing over?

How does this differ from metaphase in mitosis?

Mitos is

Independent Assortment

After the 1st Division

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__unique_features_of_meiosis.html

• Features unique to meiosis

Mitosis versus Meiosis

What happens to the possible combinations when crossing over occurs?

Sperm versus the Egg