Cell Reproduction Mitosis Chromosomes Made of

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 (2 n)

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

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 • G 1 phase – cell grows to mature size • S phase – DNA replication • G 2 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.