Monday February 1, 1999
Announcements: Review Session tonight at 110 Wartick Lab, from 6:30-7:30

Lecture notes:

Prokaryotes: (no nucleus) divide by binary fission. One piece of DNA divides, there are no organelles to separate.

Mitosis: the mechanism by which eukaryotic cells of the new generation receive a duplicate of the parental DNA.

Cytokinesis: dividing up of the cytoplasm. This happens in late anaphase or telophase.

Chromosomes: pieces of DNA with attached DNA proteins. A cell of a species can have as many as 1,000. Usually that are 10-50.

Sister Chromatids: duplicated DNA.

Centromere: the area where sister chromatids are attached.

Condensed chromosome: a chromosome which has coiled itself into a compact unit prior to separation of sister chromatids. (mitosis/meiosis).

Kinetochores: Chromosomal proteins that form on the sides of each centromere. They become attached to microtubules that help move chromosomes during the nuclear division processes (mitosis/meiosis).

Interphase has 3 parts: G₁ a period of growth and synthesis of new cell parts.
S "sythesis" phases - the DNA replicates
G₂ preparation for mitosis

Mitosis: divided into 4 phases

Prophase:
1. Condensation of chromatin into visible sister chromatids with centromeres.
2. Nucleolus disassembles.
3. Microtubules disassemble and create spindles.
4. Centrioles, if present, separate and go to poles.

Metaphase:
1. Nuclear envelope has disintegrated.
2. Chromatids line up at the equator of the cell with sister chromatids at right angles to the spindle.

Anaphase:
1. Sister chromatids separate.
2. Each chromatid is pulled toward the "poles" by spindle microtubules attached to the kinetochore on each
centromere.

Telophase:
1. The spindle apparatus disappears.
2. Chromosomes "decondense"
3. Nuclear envelope reappears.

Cytokinesis devides up the cytoplasm and make two new cells. It occurs during late anaphase and throughout telophase.

In "protists" and in animals, remnants of part of the spindle apparatus contracts to form a "cleavage furrow". This continues to contract until two cells are formed.

In plants a "line" is drawn at the equator, cellulose and other membrane and cell wall parts are deposited until the "cell plate" is complete.

Meiosis: a 2 stage nuclear division in which the parental number of chromosomes in each daughter nucleus becomes
"haploid".

Haploid: contains half the number of chromosomes. (one of each "homologous pair")

Homologous chromosomes: have the same length, shape, centromere location and gene sequence. They line up next to
one another during meiosis. (The x and y chromosomes pair up)

Germ cells: (like somatic cells) are diploid meaning they have 2 chromosomes of each type in the nucleus. Germ cells are
the cells that produce sperm or eggs.

Gametes: are haploid cells which arise as a result of meiosis in germ cells.

Meiosis assures a unique combination of traits in each new generation. It results in variations in physical and behavioral traits.

Prophase I: (major gene shuffling between homologous chromosomes)
1. The homologous pair.
2. Homologous are drawn together closely in a process called synapsis.
3. "Crossing over" occurs when non-sister chromosomes break and exchange corresponding segments.

Metaphase I
1. Homologous chromosomes line up at the "equator" of the cell.
2. Random assortment occurs. How each homologue pair aligns itself at the equator is another major method of gene
shuffling. For and organism with 3 chromosome pairs there are 23 or 8 different combinations of the chromosomes.
For humans with 23 pairs of chromosomes there are 223 or 8,388,608 possible combinations.

Anaphase I
1. Each homologue is separated from its partner

Telophase I
1. The haploid number of chromosomes arrives at each pole.
2. They are still duplicated at this point.
3. Nuclear membrane reforms.

Interkinesis: the time between Meiosis I and Meiosis II

Prophase II
1. Very brief phase.
2. Nuclear membrane breaks down.
3. Spindle forms.

Metaphase II
1. Microtubules attach to kinetochores.
2. All chromatids line up at the equator.

Anaphase II
1. Sister chromatids separate
2. One of each moves to opposite poles.

Telophase II
1. Nuclear envelope reforms.
2. Chromosomes "decondense"

1. Four daughter nuclei are formed
2. Each has a haploid number of chromosomes
3. Each chromosome is unduplicated
4. In spermatogenesis (sperm formation) in animals, all four haploid nuclei become sperm.
5. In oogenesis (egg formation) in animals, one nucleus becomes the egg, the other are "unused"

1. Mitosis produces clones.
2. Meiosis is a nuclear division that occurs in germ cells destined to become sperm or eggs. It is a reduction division used for sexual reproduction in plants and animals.
3. Meiosis ----> 2 divisions.

1. DNA duplicates
2. Chromosomes condense
3. Centromeres and kinetochores
4. Sister chromatids
5. Processes are almost identical