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I. Types of Cells
A. Somatic (Body Cells)
- Have 46 Chromosomes
B. Gametes (Sex Cells)
- Egg & Sperm
- Have 23 Chromosomes
II. Cell Growth & Limiting FactorsA. 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.
MEIOSISI. 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.