Bio Mitosis and Meiosis Notes
10/21/19
1. Types of Cell Division
a. Eukaryotic organisms
i. Mitosis
ii. Meiosis
b. Prokaryotic organisms
i. Prokaryotic fission
c. Goal of All Cell Division
i. To create new, fully functional cells
ii. Requires duplication of:
1. Organelles
2. Ribosomes
3. Enzymes
4. Complete Set of Chromosomes
2. Roles of Mitosis
a. Multicelled organisms
i. Growth
ii. Cell replacement
b. Some protistans, fungi, plants, animals
i. Asexual reproduction
3. Problem with Dividing DNA
a. Stretched out, the DNA from one human somatic cell would be more than
two meters long
b. A single line of DNA from a salamander cell would extend for ten meters
4. How do you separate so much DNA in such a small space???
a. By coiling the DNA into Chromosomes
5. Chromosome
a. A DNA molecule & attached proteins
b. Duplicated in preparation for mitosis
6. Cell Cycle
a. Cycle starts when a new cell forms
b. Two Parts:
i. Interphase--time of growth and duplication of organelles, enzymes & DNA
ii. Cell Division—separation
7. Control of the Cycle
a. Once S begins, the cycle automatically runs through G2 and mitosis
b. The cycle has a built-in molecular brake in G1
c. Cancer involves a loss of control over the cycle, malfunction of the “brakes”
8. Stopping the Cycle
a. Some cells normally stop in interphase
i. Neurons in human brain
ii. Arrested cells do not divide
b. Adverse conditions can stop cycle
i. Nutrient-deprived amoebas get stuck in interphase
Bio Mitosis and Meiosis Notes
10/21/19
c. Mitosis
i. Period of nuclear division
ii. Usually followed by cytoplasmic division
iii. Four stages:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
d. Early Prophase - Mitosis Begins
i. Duplicated chromosomes begin to condense
e. Late Prophase
i. New microtubules are assembled
ii. One centriole pair is moved toward opposite pole of spindle
iii. Nuclear envelope starts to break up
f. Transition to Metaphase
i. Spindle forms
ii. Spindle microtubules become attached to the two sister chromatids
of each chromosome
g. Metaphase
i. All chromosomes are lined up at the spindle equator
ii. Chromosomes are maximally condensed
h. Anaphase
i. Sister chromatids of each chromosome are pulled apart
ii. Once separated, each chromatid is a chromosome
i. Telophase
i. Chromosomes decondense
ii. Two nuclear membranes form, one around each set of
unduplicated chromosomes
j. Results of Mitosis
i. Two daughter nuclei
ii. Each with same chromosome number as parent cell
iii. Chromosomes in unduplicated form
k. Cytoplasmic Division
i. Usually occurs between late anaphase and end of telophase
ii. Two mechanisms
1. Cell plate formation (plants)
2. Cleavage (animals)
Meiosis
1. Aphid Sex
a. Females are produced from unfertilized eggs in summer
b. Males are produced as autumn approaches & are involved in sexual reproduction
Bio Mitosis and Meiosis Notes
10/21/19
c. Females that survive long enough, can overwinter and begin a second round
of producing new females in spring
2. Sexual Reproduction
a. Involves
i. Meiosis
ii. Gamete production
iii. Fertilization
b. Produces genetic variation among offspring
c. Provides selection for best combination of genes and helps eliminate mutations
3. Homologous Chromosomes Carry Different
Alleles
a. Human cells have two of each chromosome
b. One chromosome in each pair from mother, other from father
c. Paternal and maternal chromosomes carry different “alleles” – versions of a gene
d. Meiosis randomly distributes the alleles to the gametes
4. Chromosome Number
a. Sum total of chromosomes in a cell
b. Body & Germ cells are diploid (2n)
c. Meiosis halves chromosome number to make gametes (sperm/eggs) that
are haploid (n)
5. Meiosis: Two Divisions
a. Two consecutive nuclear divisions
i. Meiosis I
ii. Meiosis II
b. DNA is NOT duplicated between divisions
i. start w/ 46 duplicated chromosomes
ii. end w/23 unduplicated chromosomes
c. Four haploid nuclei are formed
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