Meiosis PowerPoint Notes
Integrated Science 2
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Meiosis: The Formation of Sex Cells

You simply cannot combine an egg and sperm if they contain the
number of
!

The chromosome number must be reduced to
. This is
!
I. Overview of Meiosis
A. All organisms inherit

complete sets of genes, one from
In animals, mom’s set of genes comes from an
.
cell; dad’s set of genes comes from a
cell

In plants, the genes come from
B. Sex cells, or
and
contain
.
of the normal amount of chromosomes.
1. Meiosis is the process of creating
(N) gametes from

Occurs in eukaryotic cells only

Required for sexual, but not asexual reproduction
(2N) cells
II. Chromosome Number
A. Eukaryotic sexual reproduction results in organisms with two sets of chromosomes
1. The two sets are said to be
a. chromosomes in one set have a
B. A cell with both sets of
1. Ex.
C. A cell with one set of
1. Ex.
Each body cell of a fruit fly has 8 chromosomes, 4
from the male and 4 from the female
of themselves in the other set.
is said to be
.
(liver cell, heart cell, skin cell etc.)
is said to be
.
(egg and sperm or ovule and pollen)
Each body cell of a human has 46 chromosomes, 23
from the male and 23 from the female
III. Phases of Meiosis:
Overview: Diploid cells destined to become gametes go through
rounds of cell division.
A. DNA Replication
1. occurs before the
round of cell division. (Recall interphase of mitosis)
B. Meiosis I
1. newly synthesized chromosomes pair up with their
, forming a
.

Ex. The chromosomes containing the gene for eye color from mom will pair up with the chromosome
containing the gene for eye color from dad.

This is different from mitosis!
2. the tetrads may
portions of their chromatids in a process called


are exchanged between homologous chromosomes
this introduces
!
3. Homologous chromosomes
4.
and the cell
new
(N) cells are formed, each having a unique set of genes.
C. Meiosis II
1. Performed by the two new cells produced in

each of the new haploid cell’s chromosomes contains 2 unique chromatids
2. DNA does
replicate!
3. Meiosis through cytokinesis occurs.
4.
unique

(N) cells are formed
two from each of the cells produced in meiosis I.
Males vs. Females

The formation of sperm cells is called

The formation of egg cells is called

For animals, meiosis in males produces
sperm from every germ cell vs.
- In females, 3 polar bodies
(except DNA) and
.
IV. Mitosis vs. Meiosis
A. Mitosis


reproduction
Results in the formation of
- Begins with a diploid cell (2N)
cells (2N) that are genetically
to each other and to the original cell
B. Meiosis


egg for females.
reproduction
Results in the formation of
from each other and the original cell
- Begins with a diploid cell (2N)
cells (N) that are genetically