MEIOSIS
LINDA HEIDENRICH
BIOLOGY
ALL ABOUT MEIOSIS
Occurs in sex organs (testes and
ovaries)
Cuts the chromosome number in half
Has two stages: Meiosis I and Meiosis II
Follows PMAT
Entire process preceded by
INTERPHASE and succeeded by
CYTOKINESIS
PROPHASE I
Just like mitosis
Nuclear envelope disintegrates
Chromosomes become visible and
pair with homologous
chromosomes to form a tetrad
Spindle fibers appear
METAPHASE I
Homologous chromosomes align at
the center of the cell
http://en.wikipedia.org/wiki/Meiosis
ANAPHASE I
Homologous chromosomes move
to opposite poles of the cell
http://en.wikipedia.org/wiki/Meiosis
TELOPHASE I
Nuclear membranes reform
Spindle fibers disappear
DIFFERENCE: Chromosomes remain
visible
http://en.wikipedia.org/wiki/Meiosis
MEIOSIS II (MITOSIS)
REVIEW:
Prophase: Nuclear envelope disappears,
spindle fibers form
Metaphase: Chromosomes align in the
center of the cell
Anaphase: Sister chromatids separate to
different poles of the cell
Telophase: Nuclear envelope reforms,
spindle fibers disappear, chromosomes
become invisible
NONDISJUNCTION
Term for what happens when
homologous chromosomes or sister
chromatids fail to split.
Leads to trisomy (extra chromosome)
or monosomy (too few chromosomes)
http://en.wikipedia.org/wiki/Nondisjunction
 http://en.wikipedia.org/wiki/Down_syndrome