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• Meiosis – germ cell go through 2 nuclear
divisions that results in 4 daughter cells
with half the number of chromosomes as
the parent cell.
– Explains how gametes are produced
• daughter cells are not genetically alike.
– may have different combination of genes
• Sexually reproducing organisms are capable
of combining chromosomes from 2 parents
to produce offspring.
• The chromosomes that combine during
sexual reproduction are contained in
reproductive cells called gametes.
Control of the Cell Cycle
Activity: 25 point extra creditGo to the onion root tip activity and complete the percentages activity.
Mitosis Rap
Mitosis Animation and Tutorial
Mitosis vs Meiosis
• like mitosis, meiosis follows
Interphase and
ends with cytokenisis
• The 1st meiotic division results in two cells
with ½ the number of chromosomes as the
parent cell.
• The 2nd meiotic division is like mitosis; the
number of chromosomes does not get
reduced. Results in 4 daughter cells with
half the # of chromosomes as the parent cell
Prophase I
• each chromosomes consist of
two sister chromatids connected
at the centromere
• Homologous pairs of
chromosomes come together,
this event is called synapsis
• Each pair of homologous
chromosomes is called a tetrad.
(4 chromatids that make up a
homologous pair)
• Crossing over –
exchange of genes
between non- sister
chromatids of a
homologous pair
• results in genetic
recombination by
producing a new mixture
of genetic material.
Metaphase I
• Homologous pairs (tetrads) align in
the middle of the cell.
Anaphase I
• homologous pairs separate
and move to opposite ends of
the cell.
– Each chromosome consist
of 2 chromatids
Telophase I
• Spindle fibers break down
• 2 new nuclei form
– One around each set of
– ½ the number of
chromosomes as the
original (parent) cells
– End of Meiosis I
Meiosis II
Prophase II
• Spindle fibers form
Metaphase II
• chromosomes line up at the equator
Anaphase II
• sister chromatids separate at the
centromere and move to opposite poles
Telophase II
• 4 new nuclei appear; one around each
set of chromosomes
• followed by
• end up with 4 cells that are all haploid
with only 1 chromatid for each
• Review
Meiosis - Males
Meiosis in Females
• Meiosis II
• prophase II: spindle fibers attach to the duplicated
chromosomes and begin moving them to the spindle
• metaphase II: chromosomes align at the cell equator
with one chromatid facing one pole and the other
chromatid facing the opposite pole.
• anaphase II: the chromatids separate and are now
called chromosomes. The chromosomes migrate
toward the two poles.
• telophase II: the chromosomes arrive at the opposite
poles, and the cytoplasm divides. The two meiotic
divisions result in four haploid cells.