Meiosis - the production of haploid cells with unpaired
chromosomes - word means "to diminish".
Key points of Meiosis
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The process results in 4
daughter cells
Daughter cells are haploid
Daughter cells have unique
combinations of chromosomes
Daughter cells do not have
homologous pairs
Meiosis creates gametes
(sperm and eggs)
Meiosis ensures variability in
offspring
Independent Assortment and CrossingOver
Crossing-Over occurs during prophase I
- two homologous chromosomes switch
peices of each other. This adds to the
variability of the gametes formed.
Independent Assortment
Depending on how the chromosomes
arrange themselved during metaphase I,
the cells formed can have a variety of
different chromosome combinations.
Meiosis occurs in two stages - Meiosis I and Meiosis II
The stages are similar to mitosis.
STEP BY STEP
Prophase I - homologous pairs join
together - Crossing over can occur
Pairs are called a TETRAD
Metaphase I - homologous pairs line up
along the equator. Spindle Completely
formed, fibers arrange tetrads.
Anaphase I - homologous pairs separate
Telophase & Cytokinesis - two daughter
cells are formed, these daughter cells are
haploid and do not contain homologous
pairs
Prophase II - cell prepares for second
division. New Spindle forms
Metaphase II - chromosomes line up along
the equator
Anaphase II - sister chromatids separate
Telophase II & Cytokinesis - two daughter
cells are formed from each parent cell - for
a total of FOUR haploid cells
Life Cycles
Haploid Life Cycle (protists, algae, fungi)
Diploid Life Cycle (animals)