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Class Notes
Sexual Reproduction
Meiosis
Interphase (not part of mitosis)
• Cell goes about its regular business
• Copies are made of all the cells organelles
• In the S stage of Interphase:
– Each DNA Strand makes an exact copy of itself
• The two identical strands are joined together by a
centomere.
• The joined strands are called sister chromatids
Prophase I
• Sister chromatids become visible in the
nucleus
• The nuclear membrane disappears
• Sister chromatids form homologous pairs.
Each pair is made of two sets of sister
chromatids. The pairs swap genetic
material.
Homologous pair
Metaphase I
• Spindle fibers pull the homologous pairs to
the center of the cell. Each homologous pair
is made of two sets of sister chromatids The
pairs line up opposite each other.
Anaphase
• The cell elongates
• The spindle fibers pull apart the homologous
pairs and drag them to opposite sides of the
cell.
Telophase I
• The spindle fibers disappear
• The nuclear membrane forms around the
chromatids
• A cell membrane/ cell wall forms down the
center of the cell
• Two similar cells are created.
Interphase
The cell makes copies
of all its organelles.
The chromosomes
DO NOT replicate.
Meiosis II
Prophase II
• Nuclear membrane breaks apart.
Metaphase II
Spindle fiber appear at each end of the cell and
pull the sister chromatids to line up along the
center.
Anaphase II
• Spindle fibers pull apart the sister chromatids
and pull the chromosomes toward each side
of the cell.
Telophase II
• Spindle fibers disappear.
• A nuclear membrane forms around the
chromatids.
Cytokinesis
The cytoplasm divides.
4 haploid cells are produced.
Each contains ½ the original
number of chromosome.
These are sex cells.(egg/sperm)
Meiosis Square Dance
https://search.yahoo.com/yhs/search?p=meios
is+square+dance+with+lyrics&ei=UTF8&hspart=mozilla&hsimp=yhs-001
Tune 2
http://tune.pk/video/3073786
Fertilization
A sperm and an egg cell each have ½ the
number of chromosomes as the parent cell.
When an egg and a sperm are combined,
fertilization occurs. The homologous
chromosomes from each parent combine
together to create one new cell called a zygote.
Once the egg is fertilized, the two haploid sex
cells return to being one diploid cell.
Compare Mitosis and Meiosis
Comparing Meiosis and Mitosis
Characteristic
Mitosis
Meiosis
Chromosomes
Sister chromatids
line up (2)
Homologous pairs
of chromosomes
line up (4)
No
Yes
Number of Cell
Divisions
1
2
Number of
Daughter cells
2
4
Comparison to
parent cell
Diploid
(same number of
chromosomes as
original)
Haploid
(1/2 the number of
chromosomes as
the original
Type of cells that
result
All other cells
Sex cells
(sperm/egg)
Crossover occurs
Vocabulary
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Homologous pairs
Egg
Sperm
Zygote
Diploid
Haploid
Meiosis