A. Mitosis - the division of a cell's nucleus resulting in two daughter nuclei, each with the same number of chromosomes as the original nucleus

B. Meiosis - the division of a cell's nucleus, ultimately resulting in four daughter nuclei, each with half as many chromosomes as the original nucleus.

C. Cytokenesis - cell division; frequently occurs after mitosis or meiosis

D. Functions of mitosis - growth, development, repair, reproduction in many unicellular species

E. Function of meiosis - formation of gametes in many species

F. Chromosomes

1. consist of one long DNA molecule and many proteins
2. located in the nucleus
3. the DNA molecule of a chromosome contains the genetic code
4. genes are segments of a chromosome's DNA
5. humans - 46 chromosomes in most body cells; 23 chromosomes in gametes
a. 2n = 46
b. diploid number is 46
c. n = 23
d. haploid number is 23
6. Drosophila - 8 chromosomes in most body cells; 4 chromosomes in gametes
a. 2n = 8
b. diploid number is 8
c. n = 4
d. haploid number is 4
7. chromatin - the form that chromosomes are in most of the time; "uncoiled chromosomes"
8. chromosome structure (see text p. 199)
a. nucleosomes
b. histones
c. tightly coiled chromatin
9. homologous pairs of chromosomes
a. look similar - size, shape, banding pattern
b. contain similar (but not identical) information
c. one of each pair inherited from mother (in egg)
d. one of each pair inherited from father (in sperm)
e. alleles - different forms of the same gene
10. autosomes - all the chromosomes that determine sex within a species
a. human male - XY
b. human female - XX
11. karyotype - a representation of all the metaphase chromosomes of a cell

G. The Cell Cycle

1. interphase (G1, S, G2) and mitosis (M)
2. G1 cell growth; may be long or short; may or may not lead to S
3. S - DNA is replicated
4. G2 - cell prepares for mitosis; centrosome replication
5. interphase is longer than mitosis

H. Mitosis

1. prophase
a. centrosomes migrate to opposite poles of cell
b. mitotic spindle forms
- mitotic center
- polar microtubules
c. chromatin coils and condenses to form chromosomes
2. prometaphase
a. nuclear lamina and nuclear envelope break down
b. spindle enters nuclear region
c. kinetochore microtubules
d. motor proteins - at junction of kinetochores and microtubules
3. metaphase
a. all chromosomes aligned along equator of cell
b. metaphase plate (equatorial plate)
4. anaphase
a. sister chromatids separate and move to opposite poles of cell; motor proteins; microtubules shorten

5. telophase
a. spindle breaks down
b. chromosomes uncoil to form chromatid
c. nuclear envelope forms around each set of chromosomes
6. cytokenesis usually follows telophase; each new cell is then in interphase

I. Regulation of cell cycle

1. internal control
a. cyclin - dependent kinase (Cdk)
b. cyclin
c. cyclin - Cdk complex
d. some cancers are caused by malfunctions in system of cyclins and Cdks.
2. external control
a. growth factors
- platelet-derived growth factor
- interleukins
- erythropoientin
b. some cancers are caused by malfunctions involving growth factors

J. Meiosis

1. includes two nuclear divisions - meiosis I and meiosis II
2. chromosome number is reduced from haploid to diploid
3. takes longer than mitosis
a. human males - ca. 1 month
b. human females - ca. 10-50 years
4. Where does it occur in humans?
a. males - testes
b. females - ovaries
5. interphase
a. growth
b. replication of DNA
6. prophase I
a. chromatin condenses into chromosomes
- each consists of 2 chromatids
b. centrosomes migrate
c. mitotic spindle forms (late)
d. synapsis - homologous pairs come together
- cynaptomemal complex
- chiasma
- crossing over
- independent association
- humans: 2²³ = ca. 8 million
7. prometaphase I
a. nuclear lamina and nuclear membrane break down
b. spindle enters nuclear region
8. metaphase I
a. homologous pairs line up along metaphase plate
b. different from metaphase of mitosis
9. anaphase I
a. homologous pairs separate
b. more toward opposite poles of cell
c. sister chromatids remain attached
d. different from anaphase of mitosis
10. telophase I
a. spindle may or may not break down
b. chromosomes may or many not uncoil
c. nuclear membrane may or may not reform
11. interphase II
a. short of even non existent
b. no replication of DNA
c. different from interphase I of meiosis
12. meiosis II is very similar to mitosis, but it starts with half as many chromosomes

Y. Meiosis increases genetic variation

1. crossing over - new combinations of alleles on chromosomes
2. random assortment - new combinations of chromosomes in gametes
3. fertilization - new combinations of chromosomes in zygote

Z. There is a great diversity of life cycles among species

1. gametic meiosis - meiosis results in gametes; diplody dominates life cycle (most animals, some protists)
2. zygotic meiosis - meiosis occurs right after formation of zygote; hapoidy dominates life cycle (most fungi; some protists)
3. intermediary meiosis - life cycle includes both haploid and diploid stages of significant duration (plants, some protists)

K. Spermatogenesis of Oogenesis

1. 4 sperm produced per bout of meiosis
2. 1 egg produced per bout of meiosis
a. unequal distribution of cytoplasm
b. polar bodies

L. Variety of organismal life cycles

1. reproduction - producing more individuals
2. sex - recombination of genetic material
3. asexual reproduction (cloning)
a. examples
- binary fission
- budding
- parthenogenesis
4. sexual reproduction
a. internal fertilization
b. external fertilization
5. separation of time of sex and reproduction
a. example - conjugation in bacteria
6. alternation of generations
a. life cycle includes haploid and diploid individuals
b. at most general, includes sexuality reproducing organisms
c. some species have complex life cycles

M. Chromosomal anomalies

1. aneuploidy
a. nondisjunction in meiosis I or II
b. Down syndrome (trisomy 21)
c. Turner syndrome (XO)
d. Klinefelter's syndrome (XXY)
e. Triple-X syndrome (XXX)
f. Jacob's syndrome (XYY)
g. many instances result in nonviable offspring
2. polyploidy - individuals have three or more complete sets of chromosomes