Cell Division

To replace old/damaged cells Cells divide… To replace old/damaged cells Or To reproduce

Prokaryotic cell division Called binary fission (form of asexual reproduction) Only 3 stages a) DNA replicates b) cell growth c) new cell wall forms & divides the cell **remember prokaryotes are single celled bacteria & they don’t have a nucleus!!!!!!!

Eukaryotic cell division Eukaryotes have a cell cycle. Eukaryotes have 2 different types of cell division. 1) mitosis – forms 2 diploid cells identical to the parent cell 2) meiosis – forms 4 haploid gametes that are genetically different from the parent cell

THE CELL CYCLE Interphase – growth stage * longest phase * has 3 phases 1) G1 = cell growth 2) S = DNA replication 3) G2 = new organelles, prep for division

2) Mitosis (M phase)- division of the nucleus * the nucleus & DNA divided * 4 phases of mitosis 1) prophase 2) metaphase 3) anaphase 4) telophase

Mitosis

3) Cytokinesis – the cell divides into 2 cells and each will start on their cell cycle * different for plant & animal cells

Cell cycle

Meiosis Used in spermatogenesis & oogenesis. 2) Forms the gametes needed for sexual reproduction 3) The gametes will be haploid (have ½ the number of chromosomes)

2 main stages of meiosis Meiosis I * has 4 phases (P, M, A, T) * the parent cell produces 2 diploid cells (similar to mitosis) * Major difference = crossing over in prophase I produces new combination of genes!!

Crossing over

Meiosis II * has 4 phases (same as mitosis & meiosis I) * Major difference – during anaphase II –the sister chromatids split * end up with 4 haploid genetically different gamete cells (sperm or egg)

Meiosis

Asexual vs. Sexual reprod. No exchange of genetic information. The offspring are genetically identical to the parent cell. No meiosis (no gametes!) 2 parents exchange genetic information. Offspring has a combination of genes from both parents. Sperm fertilizes egg (gametes produced during meiosis)