Download crossing over

MEIOSIS
• cell division
• one parent cell
becomes two identical
daughter cells
• cell division
• one parent cell creates
four unique cells, each
with HALF the DNA
• occurs in somatic cells
(regular cells)
• occurs in germ cells
/gametes
• used for growth and
repair
• used for sexual
reproduction
• produces sperm cells and egg cells
• occurs in two stages
MEIOSIS I: separation of homologous chromosomes
MEIOSIS 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
• 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
• 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
• 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 begins immediately
NO INTERPHASE
• Nuclear envelope dissolves, centrioles
appear, spindle fibers form
• PROMETAPHSE: chromosomes move
toward the center of the cell
• Individual chromosomes(sister
chromatids) line up at the metaphasal
plate
• Sister chromatids separate and move to
opposite ends of their cells
• Because of crossing over, each chromatid
has its own unique DNA
• Nuclear envelopes form around the new
chromatids
• Each new cell has its own unique DNA
and contains half of the organism’s DNA