MEIOSIS

MITOSIS• cell division• one parent cell

becomes two identical daughter cells

• occurs in somatic cells(regular cells)

• used for growth and repair

MEIOSIS• 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 chromosomesMEIOSIS II: separation of sister chromatids

• (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

PROPHASE I

• Chromosome PAIRS line up at the metaphasal plate

Tetrad: pairs of chromosomes

• CROSSING OVER can occur between chromosome pairs

METAPHASE I

• 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

• 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

ANAPHASE I

• Two daughter cells are created – each with HALF of the organism’s DNA• Each new cell is unique

• Cytokinesis: the separation of cytoplasms

TELOPHASE I

• Prophase II begins immediately NO INTERPHASE

• Nuclear envelope dissolves, centrioles appear, spindle fibers form• PROMETAPHSE: chromosomes move

toward the center of the cell

PROPHASE II

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

METAPHASE II

• Sister chromatids separate and move to opposite ends of their cells

• Because of crossing over, each chromatid has its own unique DNA

ANAPHASE II

• Nuclear envelopes form around the new chromatids

• Each new cell has its own unique DNA and contains half of the organism’s DNA

TELOPHASE II

EMBRYONIC DIFFERENTIATIONDUE TOMORROW