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Meiosis
The beginning of Genetics
Meiosis vs. Mitosis
• Mitosis is used to make duplicate cells for growth, repair and replacement.
• Meiosis is used to make sex cells– For example: Eggs and Sperm
• Mitosis ends with the exact number of chromosomes as it began with
• Meiosis reduces the number in half– Meiosis is also referred to “reduction division”
Interphase1. Cell starts out as a
DIPLOID cell. Either a SPERMATOCYTE or an OOCYTE
2. Chromosomes replicate.
3. Chromosomes cannot be seen
Nucleus
Cell Membrane
Prophase I1. Nucleus starts to
disappear.
2. Sister Chromatids pair up to form chromosomes, which now can be seen.
3. Homologous Chromosomes pair up to form tetrads.
4. Centrioles duplicate and move to the poles
Centromere
What kind of cell is this?
0% 0%0%0%
1. Haploid2. Diploid3. Homologous4. None of the above
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Metaphase I1. Spindle Fibers
appear.
2. Tetrads line up along the middle of the spindle.
3. Fibers attach to centromere.
Spindle Fibers
Anaphase I1. Spindle fibers pull
the tetrads apart
2. Chromosomes are pulled to the centrioles.
Telophase I
1. Spindle Fibers and centrioles disappear.
2. Nucleus reappears around each of the new sets of chromosomes.
3. Cell starts to form a break at the middle and starts to pinch in at the sides.
Telophase I (continued)
4. Cell continues to split at the mid-line forming two cells. This cell splitting is called cytokinesis
Meiosis II
Continues with both cells, but this will only show one
Prophase II1. Chromosomes are
already visible
2. Nucleus disappears
3. Centrioles move to the poles
Metaphase II
1. Spindle Fibers appear
2. Chromosomes are lined up along middle of cell
Anaphase II1. Chromosomes
are pulled apart to the centrioles
Telephase II1. Spindle fibers and
centrioles disappear
2. A nucleus appears around each set of chromosomes
3. Cell starts to pinch in at the center
Telephase II (Continued)
• Both cells divide (cytokinesis), leaving 4 new cells
• Each with half the number of chromosomes the original cell had.
• Each cell is now HAPLOID, called a gamete.• Gametes can a be a sperm or an egg.
In what cells does meiosis occur?
0% 0%0%0%
1. Skin
2. Hair
3. Reproductive organs
4. All of the above
25
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Which of the following is a gamete?
0% 0%0%0%
1. Sperm
2. Egg
3. Sex Cell
4. All of the above
25
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