Chapter 6- Chromosomes and Cell
Reproduction
I. Chromosomes
A. New cells are formed by cell
division.
1.
An adult human body produces about 2 trillion cells
EVERY day! This is about 25 million new cells per
second!

2.

3. Eukaryotic organisms undergoing growth,
development, repair, or asexual reproduction divide by
a different type of cell division.
Cell division allows for this.
Continued

4. Gametes are reproductive cells (egg and
sperm) undergo meiosis for cellular division.
B. Bacterial cells divide to
reproduce
1.
Bacteria reproduce by a type of cell division
called binary fission.

2.
Binary fission is a form of asexual
reproduction that produces identical offspring.
3. In asexual reproduction a single parent passes
exact copies of its entire DNA to its offspring.
C. Eukaryotic cells form
chromosomes before cell division

1. A gene is a segment of DNA that codes for
a protein or RNA molecule.
2. As a Eukaryotic cell prepares to divide, the
DNA and the proteins associated with DNA coil
into a structure called chromosomes.
Continued

3. Chromosomes are squished together called
chromatids.
4. The chromosome has two strands – one
from mom and one from dad. A “twist tie”
called a centromere holds them together. See
page 119.
Centromere
D. Chromosome number and
structure affect development.

1.
Each human somatic (any cell besides sex
cells) normally contain two copies of 23
chromosomes for a total of 46 chromosomes.

2.
Each chromosome contains thousands of
genes that play important roles in determining
how a person’s body develops and functions.
Continued

3. Each of the 23 pairs of chromosomes
consists of two homologous chromosomes.

4. Homologous chromosomes are
chromosomes that are similar in size, shape
and genetic content.
Continued

5. All of the cells in the body, besides gametes
have two pairs of chromosomes. (One from
mom one from dad) they are called diploid.

6. Sex cells only have DO NOT have a pair,
they are called haploid (1/2 the amount of
chromosomes)
Continued
7. A zygote is a fertilized egg cell.

8. Look at figure 6-1 pages 121 to view
number of chromosomes.
E. Chromosomes determine your
sex.

1.
Of the 23 pairs of chromosomes in human
somatic cells, 22 pairs are called autosomes

2.
Autosomes are chromosomes that are not directly
involved in determining the sex of an individual.

3.
The sex chromosomes, one of the 23 pairs
contain the gene that determines the gender. Males
determine the gender of the human.
F. Change in chromosome number

1.
Sometimes a human could have different
chromosome numbers.

2.
A karyotype is performed to view an individual’s
chromosomes.

3.
Down syndrome is an extra copy on pair 21.
II. The cell Cycle
A. The cell cycle describes the life of a Eukaryotic cell.

1. The cell cycle is a repeating sequence of cellular
growth and division during the life of an organism.

2. A cell spends 90% of its time in the first three
phases of the cycle-interphase.
Continued

3. First growth (G1)phase- a cell grows rapidly
and carries out its routine functions. Cells that
are not dividing remain in the G1 phase.
4. Synthesis (S) phase- A cell’s DNA is copied
during this phase. At the end of this phase,
each chromosome consists of two chromatids
attached at the centromere.
Contined

5. Second growth (G2) phase-In the G2
phase, preparations are made for the nucleus
to divide.
6. Mitosis-the process during cell division in
which the nucleus of a cell is divided into two
nuclei.
Continued

7. Each nucleus ends up with the same number
and kinds of chromosomes as the original cell.
8. Cytokinesis-the
cytoplasm splits.
B. The cell cylce is carefully
controlled

1.
If a cell spends 90% of its time in
interphase how do cells “know” when to
divide?

2.
Cell Growth (G1) checkpoint-This
checkpoint makes the key decision of weather
the cell will divide or not.
Continued

3. DNA synthesis (G2) checkpoint-DNA
replication is checked at this point by DNA
repair enzymes. If this checkpoint is passed,
proteins help to trigger mitosis.

4. Mitosis checkpoint-will trigger the exit
from mitosis.
C. When control is lost: cancer

1.
Certain genes contain the information
necessary to make the proteins that regulate
cell growth and division.

2.
If one of these genes is mutated, the
protein may not function.
Continued

3. Cancer is the uncontrolled growth of cells.

4. Cancer is a disorder of cell division.
D. Mitosis

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Interphase (not really a phase)
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
INTERPHASE

Interphase- is part of the cell cycle before
mitosis. During Interphase
–
The cell grows
– DNA is being copied
– This period between cell division can be very long.
INTERPHASE
PROPHASE

Prophase- This is the longest phase. During
this phase;




The nuclear envelope disappears.
The centrioles start to move to the opposite poles.
Spindle fibers start to form.
Chromosomes are becoming evident.
PROPHASE
METAPHASE

Metaphase-Metaphase is the shortest phase
of mitosis.

The chromosomes line up in the middle of the cell.
METAPHASE
ANAPHASE

ANAPHASE- Begins when the centromere that
join the sister chromatids start to split.

The chromosomes are being pulled to the opposite sides
of the cell toward the Centrioles.
ANAPHASE
TELOPHASE

TELOPHASE-Final process of mitosis.


Chromosomes are at the opposite poles.
Nuclear envelope reforms.
TELOPHASE
CYTOKINESIS-Splitting of the
cytoplasm.
Teacher note:
http://www.cellsalive.com/mitosis.htm