Chapter 10: Cell Division Before a cell divides, its Chromosomes replicate and the nucleus divides.

Chromosome Structure  DNA coils and wraps around proteins called histones  An isolated chromosome consists of two identical halves called chromatids connected at the center by the centromere.

Chromosome Types  Sex chromosomes: determine the gender of an organism and also carry other genes.  Autosomes All the other chromosomes that exist for an organism All the other chromosomes that exist for an organism Occur in pairs called homologues or homologous chromosomes (one from each parent) Occur in pairs called homologues or homologous chromosomes (one from each parent)

Chromosome number  Diploid (2n) Cells that contain both sets of chromosomes Cells that contain both sets of chromosomes All body cells (not sex cells) are diploid in number All body cells (not sex cells) are diploid in number For humans, this number is 46 For humans, this number is 46 For humans, this number is 46 For humans, this number is 46  Haploid (1n) Cells that only contain one of the pair Cells that only contain one of the pair Reproductive cells (=sex cells=gametes=sperm or egg) Reproductive cells (=sex cells=gametes=sperm or egg) For human gametes, this number is 23 For human gametes, this number is 23

Cell Division  Prokaryotic cells divide by binary fission  Eukaryotic cells undergo a cell cycle: cell cyclecell cycle Interphase Interphase M phase (mitosis) M phase (mitosis) cytokinesis cytokinesis

Stages of Mitosis Stages of Mitosis  Prophase Prophase  Metaphase  Anaphase  Telophase

Cytokinesis: follows telophase forming 2 resulting cells  Plant cells: a cell plate forms first  Animal cells: the cell membrane pinches inward and forms a cleavage furrow Animal cells Animal cells

Two ways to reproduce  Asexually: result of one parent  Sexually: offspring from the union of egg and sperm (2 parents)

MeiosisMeiosis: the division of nuclei in the formation of gametes Meiosis  Meiosis I Prophase I Prophase I Metaphase I Metaphase I Anaphase I Anaphase I Telophase I Telophase I  Meiosis II Prophase II Prophase II Metaphase II Metaphase II Anaphase II Anaphase II Telophase II Telophase II  Results: oogenesis and spermatogenesis oogenesis and spermatogenesisoogenesis and spermatogenesis