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Ch. 8 Cell Reproduction
What is cell division?
Mitosis
What is a zygote?
It forms when the male and female
gametes unite.
All cells come from preexisting cells
DNA is inside a rod-shaped structure
called a?
Chromosomes
Chromosomes
Every chromosome consists of two identical parts
called sister chromatids. Each half is a chromatid.
The point where each chromatid crosses or attaches to
the other chromatid is called the centromere.
Chromatids only occur during S phase of interphase.
Every cell has a certain # of chromosomes in the cell.
(Pg. 146)
Ex. Humans=46, chicken=78, cat=32, chimp=48,
dog=78
Pg. 145  Histones are proteins that DNA wraps
around in eukaryotic cells.
Why do all organisms have an even # of
chromosomes?
Chromosomes are in pairs called homologous
chromosomes.
A diploid (2N) cell has both chromosomes
that make up the homologous pair.
A haploid (1N) cell has only 1 half of the
homologous pair.
Sex chromosomes determine the sex of the
offspring (X or Y).
Autosomes are all the chromosomes except
the sex chromosomes. We have 44 or 22 pair.
Karyotype – a map of the chromosomes.
Cell Cycle
3 parts to the cell cycle
1. Interphase – resting & growth stage
(3 parts – G1, S, & G2)
2. Mitosis – cell division (4 parts)
3. Cytokinesis- produces 2 daughter
cells
Pg. 149
There are approximately 100 trillion cells
in an average human.
Some cells divide every 20 to 30 minutes
in a animal embryo.
4 Stages of Mitosis
Prophase – 1st stage of mitosis
Chromosomes start to coil and shorten.
Centrioles form and migrate to each
end.
 Animals only have centrioles from the
centrosomes. Pg. 150
Spindle fibers form between the two
centrioles.
Nuclear membrane & nucleolus break
down and disappear.
Metaphase
2nd phase of mitosis
The chromosomes are attached
to the spindle fibers.
The spindle fibers arrange the
chromosomes in a line at the
middle of the cell.
Anaphase
3rd stage in mitosis
The centromeres are pulled
apart as the spindle fiber
shortens and separates the sister
chromatids in half.
Now each chromatid is at
opposite ends.
Telophase
4th phase of mitosis
The chromatins reach the opposite
poles of the cell.
The spindle fiber & centrioles
disappear
The chromatids uncoil
The nucleolus reappears and a new
nuclear envelope forms around
each set of chromosomes.
Cytokinesis
The plasma membrane
pinches off and 2 new
identical cells are formed.
The 2 new cells are called
daughter cells.
st
Interphase(1
part of the cell
cycle)
Resting and growth stage
The chromatins are duplicated
in order to form a sister
chromatin, which is two
identical chromatins.
The cell is preparing to
undergo mitosis.
Mitosis Video
Meiosis
Reduction of Division  Meiosis
Meiosis I produces 2 daughter cells, each with
half the homologous chromosome. Go from one
cell with 46 chromosomes (2N) to two daughter
cells with 23 (1N) chromosomes. Draw. Pg.
154-155
Meiosis II occurs after meiosis I. The 2
daughter cells divide to produce 4 haploid cells.
These haploid cells are gamete cell, either egg
cells or sperm cells.
Meiosis Video
Differences in Meiosis vs. Mitosis
1. Form synapsis in prophase – homologous
chromosomes pair up.
Each pair of homologous chromosomes is called a tetrad.
2. Crossing-over occurs when the chromatids twist and
reattach to the opposite homologous chromosome in
the tetrad. Pg. 154.
3. The outcome of Meiosis I is 2 new cells with half the
number of chromosomes as the original cell, but the 2
new cells have two copies of the chromosomes because
of replication before Meiosis I.
Meiosis II does not have replication, so the final
product is 2 new cells (4 total now) with half the
chromosomes (haploid – 1N).
Genetic recombination is the result of crossingover during prophase/metaphase of Meiosis I.
This causes a mixing of genetic material.
Independent assortment – is the random
separation of chromosomes during
prophase/metaphase of Meiosis I. This causes
genetic variation of maternal and paternal
chromosomes.
Cell Division Video
Mitosis vs. Meiosis