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) C.

B. Cell size is limited.

“Bigger is not Better!” 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. G 1 - 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. G 2 - 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.

I.

MEIOSIS

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 (1 st 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 (2 nd 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.