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Meiosis
How to make SEX cells!
What is Meiosis?

Most living things have body cells and sex
cells (sperm and eggs)
– Eggs are female sex cells
– Sperm are male sex cells

Meiosis is a special cell division that
results in sex cells
What’s the Big Picture?

In meiosis, a cell divides twice making a
total of how many cells?
4
What’s the Big Picture?
1st time, each chromosome in a pair move
away from its partner, each chromosome
goes to a different cell, sister chromatids
stay joined together
2nd division – sister chromatids separate
Some Terms:
• Cells that have the normal number of
chromosomes are called “Diploid”
• Cells that have ½ the normal number of
chromosomes are called “Haploid”
• Meiosis results in 4 Haploid cells that are
genetically different from each other (and
remember the parent cell was diploid)
Some Terms:
• Cells have pairs of chromosomes each
chromosome in a pair is “homologous” to
the other (they are homologs).
• In meiosis the homologous chromosomes
separate.
Interphase I

DNA Replicates
PROPHASE 1
Nuclear membrane begins to break down
 Centrioles begin to move away from each
other
 Homologous (matching) chromosomes
come together to form “tetrads”
(remember: each chromosome has 2
strands of sister chromatids – now looks
like 4 strands)
Metaphase 1

Sister chromatids become attached to
fibers
 Homologous chromosomes move to the
center of the cell
Anaphase 1
•
Tetrads separate into double stranded
chromosomes
Telophase 1

Cell membrane pinches cell into two
 Nuclear membrane does not reform
Interphase II

DNA DOES NOT Replicate
Prophase II (2)

Centrioles double and form fibers again
Metaphase II (2)

Fibers connect chromatids and they line up at
the middle
Anaphase II (2)

Fibers pull each strand apart to opposite
ends of the cell
Telophase II (2)

Cells Divide – Now have 4 cells
–
–
–
–
Each has ½ the # of Chromososmes (Haploid)
Each is genetically different from the others
Nuclear membrane reforms
Cell pinches off
The Whole Thing
Part 1…
The Whole Thing
Part 2…