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 divisions Meiosis preceded by an interphase (just like mitosis) – chromosomes replicated during the S phase.

Meiosis 1

Stages of Meiosis

Crossing Over in Action

How does this differ from metaphase in mitosis?

Independent Assortment

After the 1 st Division

hill.com/sites/ /student_view0/ch apter28/animation__unique_features_of_mei osis.html hill.com/sites/ /student_view0/ch apter28/animation__unique_features_of_mei osis.html Features unique to meiosis

Mitosis versus Meiosis

What happens to the possible combinations when crossing over occurs?

Sperm versus the Egg