Meiosis
Cell division process whereby the number of chromosomes in
a diploid cell is reduced by half through the separation of
homologous chromosomes. This produces the gametes.
Why Meiosis?
• Meiosis
• To produce gametes (sex) cells
• Egg and Sperm cells
Terms Review…
• Haploid: (n) having a single set of
chromosomes in the cell. ex. Gametes; humans
have 23 chromosomes in sex cells (egg and
sperm cells)
• Diploid: (2n) having two sets of homologous
chromosome in the cell. ex. Somatic (body) cells;
humans have 23 pairs or 46 chromosomes in
body cells
Human Karyotype with 23 pairs of homologous
chromosomes for a diploid number of 46; 2n =
2(23) = 46
Terms Continued
• Homologous chromosomes – two sets of chromosome in a pair,
with one set coming from a male parent and the other set coming
from the female parent.
• Tetrad – pairing of homologous chromosomes during meiosis I,
and such pairing has 4 (tetra) chromatids. These chromatids
can then exchange genetic material.
• Crossing-over – process in which tetrad of homologous
chromosomes exchange portions of their chromatids, and thus
genetic material is exchanged; this occurs during Prophase I of meiosis.
• Gametes – sex cells; involved in sexual reproduction. Male gametes
are called sperm cells and female gametes are called egg cells; sperm
are produced in testes and egg are produced in ovaries by meiosis.
Crossing-Over
Section 11-4
Crossing-Over
Section 11-4
Crossing-Over
Section 11-4
Crossing Over
• What is happening?Exchange of genetic material
between homologous chromosomes
• How does this affect the individual (offspring)?
Creates genetic variation
Crossing Over
How does Meiosis Occur?
Meiosis Review
1.
Is the beginning parent cell diploid or
haploid (2n or n)?
2. Are the resulting daughter cells diploid or
haploid
(2n or n)?
More Meiosis Review
3. How many daughter cells are
produced?
4. Are the resulting daughter cells
different
from the
parent cell?
More Meiosis Review
5. Are the resulting daughter cells different
from each other?
6. How many chromosomes are in a
human parent cell?
7. How many chromosomes are in a
human daughter cell?
More Meiosis Review
8. What types of cells are
produced by meiosis?
Fertilization
Mom
Dad
23
23
46
New Individual
This is how new organisms
are made!!
Let’s review
Mitosis & Meiosis
Mitosis vs. Meiosis
Event
Mitosis
Produces 4 cells
Produces 2 cells
New cells identical
√
√
√
New cells different
New cells have the same number
of chromosomes as parent
New cells have fewer
chromosomes than parent
Meiosis
√
√
√
Mitosis vs. Meiosis
Event
Beginning cells diploid (2n)
Beginning cells haploid (n)
Ending cells diploid (2n)
Ending cells haploid (n)
Mitosis
Meiosis
√
√
√
Produces egg and sperm
Produces body cells
√
√
√