Name: _________________________________________________________ Date: _____________ Period: __________
Standard: MC.2.B.9 list and describe the stages of mitosis (prophase, metaphase, anaphase, telophase, and cytokinesis)
& MC.2.B.10 Analyze the meiotic maintenance of a constant chromosome number from one generation to the next.
Bell ringer: _________________________________________________________________________________________
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Meiosis – Sexual reproduction pg. 275
There are two cell divisions: Mitosis and Meiosis. Mitosis has one division and meiosis has two divisions. In
Meiosis, four cells are created where there was originally one. That's four (4) cells with half of the amount of DNA
needed by a cell. When a cell goes through meiosis, it's not concerned about creating another working cell. Meiosis
happens when it's time to reproduce an organism.
The steps of meiosis are very simple. When you break it down, it is just one round of Interphase followed by two
PMATC's in a row (Prophase, Metaphase, Anaphase, Telophase, and Cytokinesis). Scientists call it Meiosis I and Meiosis
II. The main difference is that during Meiosis II, the cell does not go through interphase, so DNA is not duplicated.
When do cells undergo meiosis? ______________________________________________________________________
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In meiosis, the cell divide a second time without replicating DNA. What happens to the number of chromosomes in the
cells produced in meiosis II compared to the cells produced in meiosis I?
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That second division divides the number of chromosomes in half. When you have half the number of
chromosomes, you are called a haploid cell. Haploid means half the regular number. Diploid is the opposite (two
strands). Normal cells are considered to be diploid cells.
Chromosome characteristics:
Haploid (n) = one set of chromosomes
Diploid (2n) = two sets of chromosomes
Eggs and sperm (gametes) are haploid.
Somatic cells (body cells) are diploid.
Diploid set for humans: 2n = 46
In males, meiosis results in four equal-sized gametes called sperm. In females, only one large egg cell results
from meiosis. The other three cells, called polar bodies, usually are not involved in reproduction.
Meiosis – Gamete (egg and sperm) production
Meiosis Step 1:
MEIOSIS I: This is basically like the IPMATC of a regular mitosis.
*Meiosis is a bit different because there something called crossing-over that happens to the DNA*
Crossing over is an exchange of genes. The genes are mixed up, not resulting in a perfect duplicate like
mitosis. The cell divides, leaving two new cells with a pair of chromosomes each. Normally the cell would begin to go
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about its business of living and slowly duplicate the chromosomes for another mitotic division. Since this is meiosis,
there is a very short interphase and division begins again.
Meiosis Step 2:
MEIOSIS II:
Prophase II the DNA that remains in the cell begins to condense and form short chromosomes. The centrioles also begin
to move to opposite sides of the cell.
Metaphase II all of the chromosomes line up along the center of the cell and the centrioles are in position for the
duplication.
Anaphase II shows the chromosomes split and move to opposite sides of the cell. Each one splits into two pieces. They
don't divide up the DNA between the new cells; they split the DNA that exists. Each daughter cell will get one-half of
the DNA needed to make a functioning cell.
Telophase II shows the DNA completely pulled to the sides and the cell membrane begins to pinch.
When it's all over, you are left with four haploid cells that are called gametes (egg and sperm). The eventual
purpose of the gametes will be to find other gametes with which they can combine. When they do, they will form a new
organism.
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Property
Mitosis
Meiosis
DNA replication
Number of divisions
Synapsis of homologous
chromosomes
Number of daughter cells and
genetic composition
(diploid/haploid)
Role in the animal body
What is the purpose of crossing-over?
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What are somatic cells?
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What are gametes?
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Why do gametes must have half the number of chromosomes in somatic cells?
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