Download B. Chromosomes

I.
Types of Cells
A. Somatic (Body Cells)
- Have 46 Chromosomes
B. Gametes (Sex Cells)
- Egg & Sperm
- Have 23 Chromosomes
II.
Cell Growth & Limiting Factors
A. Cell size can vary greatly.
i.e. Red Blood cells (8um) & Nerve
cells (1m)
B. Cell size is limited.
“Bigger is not Better!”
C. Diffusion
- Decreases as a cell grows.
- Will take longer for waste to exit a
cell or building blocks to enter a cell.
- Protein production is decreased. (DNA
overload)
III. Chromatin versus Chromosomes
A. Chromatin
- DNA when a cell is not dividing.
- Loosely packed DNA that is
wrapped around proteins (Histones).
B. Chromosomes
- DNA when a cell is dividing!
- Composed of tightly bound
chromatin.
Steps 1-3: DNA forms a chromosome, also
called a chromatid.
Step 4: The chromosome has replicated.
Step 5: Duplicated chromosome, before division.
IV.
Why do cells divide?
A. To replace old, worn out cells.
B. To replace injured / damaged cells.
C. For an organism to grow.
D. For reproduction to occur.
V.
The Cell Cycle
A. Growth & division of “somatic” cells.
B. A cell has 2 general periods:
1. Interphase – The growth period.
2. Division – The production of 2
“daughter” cells.
C.
Stages of the Cell Cycle:
1. INTERPHASE (3 sub-phases)
a. G1
- Period of rapid cell growth.
- Synthesize new organelles
- Lasts roughly 11 hours.
b. S
- Will begin if the “Restriction Point” is
passed.
- DNA is synthesized /
Chromosomes are copied.
- Lasts roughly 7 hours.
c. G2
- All organelles are copied
- Lasts roughly 3 hours.
D. TERMS: Chromatid & Sister Chromatids
a. Chromatid
- One identical copy of a chromosome.
b. Sister Chromatids
- Two identical chromatids connected
together by the centromere.
- Spindle fibers from centrioles
will connect to the kinetechore
(portion of centromere).
2.
MITOSIS (P.M.A.T)
STEPS:
1. Prophase
- DNA coils & becomes chromosomes
- The chromosomes have already
duplicated themselves and have 2
identical halves called
“Sister Chromatids.”
- The nuclear envelope disappears.
2. Metaphase
- The chromosomes (Sister
Chromatids) line up along the
equator.
3. Anaphase
- All sister chromatids are pulled apart
by spindle fibers from the centrioles.
- One chromatid moves to each side of
the cell.
- Remember, each cell only gets 46.
4a. Telophase
- The nucleus reappears.
- Chromosomes uncoil into
chromatin.
4b. Cytokinesis
- The cytoplasm finally breaks in two.
End Result: Two new identical cells.
Cytokinesis Vs. Mitosis
• Mitosis is division of the NUCLEUS
• Cytokinesis is division of the CYOPLASM
• In plants Cell Plate forms during
cytokinesis.
– Becomes the cell wall
VI. Chromosome Numbers
A. Diploid
- Refers to cells which carry a double
set of chromosomes.
B. Haploid
- Refers to cells with just one set of
chromosomes.
C. Homologous Chromosomes
- Refers to two chromosomes which
are similar in structure.
- Each contains the same genes.
MEIOSIS
I.
What is it?
- The formation of gametes.
- Produces 4 cells, each with half the original
chromosome number.
Comparison to Mitosis:
- 2 Cell Divisions (8 Phases).
- 4 Cells with 23 chromosomes.
- Cells are not identical.
II.
Meiosis I (1st Division)
A. Prophase I
- Synapsis occurs:
* Process of homologous
chromosomes finding each other.
- Tetrads form:
* Two pairs of homologous
sister chromatids combined
together.
- Crossing-Over occurs.
* Process where two homologous
chromosomes “exchange” genetic
information.
- Each chromatid is now different.
- Leads to variation & evolutionary
change.
(Click image for animation.)
B. Metaphase I
- 23 Tetrads line up along equator.
C. Anaphase I
- Tetrads are separated.
- Homologous chromosome pairs
moves in opposite directions.
D. Telophase I
- 2 new cells are formed.
- Each cell has 46 chromosomes, or 23
sister chromatids.
- SO…….23 X’s
III. Meiosis II (2nd Division)
A. Prophase II
- Nothing different.
B. Metaphase II
- Chromosomes line-up along equator.
- 23 X’s.
C. Anaphase II
- Centromeres break down and sister
chromatids split.
D. Telophase II
- 4 cells produced each with 23
chromosomes.
- Each cell is considered Haploid (n).
= 23 Chromosomes.
- Original cell was Diploid (2n).
= 46 Chromosomes.
VI. Possible Errors
A. Mutations
- An error or change in the DNA
sequence.
1. Non-Disjunction
- Failure of chromosomes to
separate properly during meiosis.
- Results in an extra or missing
chromosome(s).
Examples: Trisomy 21 and Turners Syndrome
B. Karyotype
A picture of chromosomes taken
during prophase of cell division.
1. Can be used to diagnose
chromosomal disorders /abnormalities.
2. 46 chromosomes break down into
23 pairs.
a. 22 pairs are referred to as
autosomes.
b. There is one pair known as the sex
chromosomes.
1. Males have an X and a Y.
2. Females have 2 X’s.
Karyptype Ex.
• Turners Syndrome
Karyotype Example
• Downs Syndrome
Karyotype Example
• Edward’s Syndrome
Syndromes:
• A few syndromes that can be detected using a
karyotype are:
• Down’s Syndrome- Usually occurs when a person
has an extra chromosome # 21
• Klinefelter’s Syndrome- Occurs when a person
has 2 X chromosomes AND a Y
• Turner’s Syndrome- Occurs when a person has
only one X chromosome and no Y
• Fragile X – Occurs when the X chromosome
appears to have a break or tear.
• Edwards Syndrome – Occurs when an individual
has an extra #18 chromosome.
• Cri Du Chat – Syndrome classified by missing all
or part of chromosome #5.