Download meiosis

Bell Ringer
1. List the stages of mitosis in order.
2. What’s the difference between a chromatid and a
centromere?
3. Why is it important for chromosomes to form before
cell division?
What are fraternal twins?
Meiosis
February 6, 2014
Biology
TWO TYPES OF
CELLS
•
Somatic Cells
•
Gametes
Somatic Cells
•
Make up most body tissues and organs.
•
NOT passed to children.
Gametes
•
Sex cells
•
Passed to children
How many chromosomes
do WE have?
1. Autosomes
•
Chromosomes that are not directly involved/related
to the sex of an organism.
•
Somatic cells
2. Homologous
Chromosomes
•
Pair of chromosomes
•
Inherit one from each parent.
•
Carry the same genes, but may code for different
traits.
Homologous Chromosomes
eye color
locus
eye color
locus
hair color
locus
hair color
locus
Paternal
Maternal
3. Sex Chromosomes
•
Contain genes that directly control the development
of sexual characteristics.
•
X and Y
Diploid Cell (2n)
•
Has TWO copies of each chromosome (from mom
and dad)
•
Somatic (body) cells typically
•
Result from MITOSIS.
Haploid Cell (n)
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Has ONE copy of each chromosome.
•
Gametes are haploid typically.
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Result from MEIOSIS.
Review: Mitosis
•
Makes genetically identical cells.
•
Makes diploid cells.
•
Takes place throughout lifetime.
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Involved in asexual reproduction.
Meiosis
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Makes genetically unique cells.
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Makes haploid cells.
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Takes place at certain times in life cycle.
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Involved in sexual reproduction.
Mitosis vs. Meiosis
MUST KNOW!
•
Makes genetically
identical cells.
•
Makes genetically
unique cells.
•
Makes diploid cells.
•
Makes haploid cells.
•
Takes place throughout
lifetime.
•
Takes place at certain
times in life cycle.
•
Involved in asexual
reproduction.
•
Involved in sexual
reproduction.
Homologous Chromosomes
•
Pair of chromosomes
•
Inherit one from each parent.
•
Carry the same genes, but may code for different
traits.
•
Separate during Meiosis I.
Sister Chromatids
•
Duplicates of each other.
•
Attached together at the centromere.
•
Separate during Meiosis II.
Meiosis I
1. Prophase I
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Chromosomes condense
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Homologs pair up.
•
Nuclear envelope breaks down.
•
Spindle fiber forms.
Prophase I
spindle fiber
aster
fibers
centrioles
How many cells do we have?
1
How many chromosomes do each
cell have? 4
Prophase I - Synapsis
Homologous chromosomes
sister chromatids
Tetrad
sister chromatids
Crossing Over - variation
nonsister chromatids
chiasmata: site of
crossing over
Tetrad
variation
2. Metaphase I
•
Spindle Fibers align chromosomes along cell
equator.
Metaphase I
OR
metaphase plate
metaphase plate
3. Anaphase I
•
Homologs separate.
•
Chromatids remain attached.
Anaphase I
4. Telophase I
•
Spindle fibers fall apart.
•
Nuclear envelope may form again.
Telophase I
How many cells do we have?
2
How many chromosomes do each
cell have? 2
Now that we’ve reduced
our chromosome number
in half, we’ve gone from
what type of cell to what?
•
Diploid to haploid
Meiosis II
5. Prophase II
•
Chromosomes condense
•
Nuclear envelope breaks down.
•
Spindle fiber forms.
Prophase II
• same as prophase in mitosis
6. Metaphase II
•
Spindle Fibers align chromosomes along cell
equator.
Metaphase II
• same as metaphase in mitosis
metaphase plate
metaphase plate
7. Anaphase II
•
Chromatids separate.
Anaphase II
• same as anaphase in mitosis
• sister chromatids separate
8. Telophase II
•
Spindle fibers fall apart.
•
Nuclear envelope forms again.
Telophase II
How many cells do we have?
4
How many chromosomes do each
cell have? 2
Review
1. What’s the difference between diploid and haploid?
2. Which processes (Mitosis and Meiosis) produce each?
3. Why is Prophase I so important?
4. When in Meiosis does the chromosome number become haploid?
5. How many cells do you end up with after a cell undergoes meiosis?
6. What are homologous chromosomes (homologs)?
7. What’s the difference between autosomes and sex chromosomes?
Independent Practice
•
Complete Meiosis Practice Worksheet. (Will check
during tomorrow’s bell ringer)
•
Complete and show Ch. 6-1,2 vocabulary (DUE
TODAY)