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.