MEIOSIS

MITOSIS MEIOSIS cell division one parent cell becomes two identical daughter cells occurs in somatic cells (regular cells) used for growth and repair cell division one parent cell creates four unique cells, each with HALF the DNA occurs in germ cells /gametes used for sexual reproduction

MEIOSIS produces sperm cells and egg cells occurs in two stages MEIOSIS I: separation of homologous chromosomes MEIOSIS II: separation of sister chromatids

PROPHASE I (DNA has already been duplicated in S phase) DNA condenses into chromosomes Nuclear envelope dissolves Centrioles appear at opposite ends of the cell; spindle fibers attach to centromeres PROMETAPHASE: chromosomes move towards the center of the cell

METAPHASE I Chromosome PAIRS line up at the metaphasal plate Tetrad: pairs of chromosomes CROSSING OVER can occur between chromosome pairs

CROSSING OVER: when chromosome pairs exchange equal amounts of DNA where they intersect CHIASMA: the point of intersection; where “crossing over” occurs Leads to increased genetic diversity

ANAPHASE I Spindle fibers contract Tetrads are broken apart into chromosomes Half of the DNA moves to one end of the pole; the other half moves to the other end

TELOPHASE I Two daughter cells are created – each with HALF of the organism’s DNA Each new cell is unique Cytokinesis: the separation of cytoplasms

PROPHASE II Prophase II begins immediately NO INTERPHASE Nuclear envelope dissolves, centrioles appear, spindle fibers form PROMETAPHSE: chromosomes move toward the center of the cell

METAPHASE II Individual chromosomes(sister chromatids) line up at the metaphasal plate

ANAPHASE II Sister chromatids separate and move to opposite ends of their cells Because of crossing over, each chromatid has its own unique DNA

TELOPHASE II Nuclear envelopes form around the new chromatids Each new cell has its own unique DNA and contains half of the organism’s DNA

EMBRYONIC DIFFERENTIATION DUE TOMORROW