P Meiosis

Meiosis “is a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell” Process – a method, a way Nuclear – nucleus – control center and instructions of the cell Division – separating, getting more Reduces – lowers Number of chromosomes - amount of DNA New cell – the ones that are being created Meiosis is a way of making a cell that has half the DNA they started with. Why? – Sexual Reproduction Every species of animal has a special number of chromosomes Humans are 46 Dogs are 78 So regular cells cant be used for reproduction

PROPHASE 1 : DNA  chromosomes Spindle appears Homologous Chromosomes find each other Crossing over occurs

METAPHASE 1: Tetrads line up Spindle fibers attach

ANAPHASE 1: Homologous Chromosomes separate and move toward opposite ends of the cell

TELEPHASE 1: chromosomes reach ends of the cell New nuclear membranes form Cytokinesis 1 occurs

PROPHASE 2: Spindle fibers form Nucleus dissolves (again) Chromosomes start moving to middle

METAPHASE 2: chromosomes (without pairs) line up in middle of cell Spindle fibers attach

ANAPHASE 2: Chromatids separate and move to opposite ends of the cell Cleavage furrow is seen

TELOPHASE 2: Chromatids make it to end of cell New nuclear membrane forms Cytokinesis 2 occurs

Gametes Cells that have half the DNA and are used for reproduction are called – SEX CELLS XX = Egg = oogenesis = 1 cell  1 egg XY = Sperm = spermatogenesis = 1 cell  4 sperm

Vocab Asexual reproduction Crossing over Gamete Independent assortment Oogenesis Sexual reproduction Spermatogenesis Tetrad Cell cycle – G1, S, G2, M