Cell Reproduction Mitosis

Chromosomes Made of DNA Wrap around histone proteins to become chromatin

Chromosomes Chromatin wind up further to become chromosomes Each half of a chromosome is a chromatid Chromatids are held together in the center at the centromere

Chromosomes Sex chromosomes determine an organism’s sex Females = XX Males = XY Number of sex chromosomes in a human cell is 2

Chromosomes Autosomes – all the chromosomes except for the sex chromosomes Number of autosomes in humans = 44

Chromosomes Homologous chromosomes – every cell in sexual organisms has two copies of each autosome

Chromosomes Humans have 44 autosomes so they have 22 homologous pairs. Dogs have 76 autosomes so they have 38 homologous pairs. –Goat = 58 –Armidillo = 62 –Chicken = 78 –House fly = 12 –Mosquito = 6

Diploid Cells with 2 sets of chromosomes (homologous prs.) are diploid. In humans, the diploid number is 46 (2n)

Haploid Cells with one set of chromosomes are haploid. In humans, the haploid number is 23 (1n).

Cell Division -Prokaryotes Bacteria do not have a nucleus. They divided by a process known as binary fission.

Binary Fission Chromosomes replicate The cell grows to twice its original size The cell divides into two identical cells

Cell Division in Eukaryotes Eukaryotes have a nucleus in their cells Mitosis: results in new cells with identical genetic material Meiosis: results in new cells with half the number of chromosomes

Cell Cycle Set of events that make up the life of a cell

Interphase Takes up most of the cell’s lifespan (up to 90%)

Interphase G1 phase – cell grows to mature size S phase – DNA replication G2 phase – cell prepares for division

Mitotic Phase Series of events that allows a cell to divide Prophase Metaphase Anaphase Telophase

Prophase DNA winds up into chromosomes Centrioles appear at opposite ends of the nucleus

Prophase Spindle fibers form Chromosomes attach to spindle fibers Nuclear membrane and nucleolus disappear

Metaphase Chromosomes move to the center (equator) of the cell

Anaphase Chromatids separate by the centromere They are now considered to be individual chromosomes

Telophase Spindle fibers disappear Chromosomes begin to unwind into chromatin Nuclear membranes begin to form

Cytokinesis Immediately follows mitotic division The cell membrane is split in half

Animal Cytokinesis The membrane pinches off into two new cells

Plant Cytokinesis A cell plate forms in the center. The plate separates the two cells.