CELL DIVISION MITOSIS: Reproducing the nucleus of a somatic cell. MEIOSIS: Producing sex cells...
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Transcript of CELL DIVISION MITOSIS: Reproducing the nucleus of a somatic cell. MEIOSIS: Producing sex cells...
CELL DIVISION
MITOSIS:
Reproducing the nucleus of a somatic cell.
MEIOSIS:
Producing sex cells (gametes).
CYTOKINESIS:
Division of cytoplasm and organelles.
MITOSIS & MEIOSIS, con’t.
Both mitosis and meiosis consist of a sequence of phases:
• interphase (preparation for division)
• prophase
• metaphase
• anaphase
• telophase
MITOSIS & MEIOSIS, con’t.
Result of Mitosis:
•formation of two daughter nuclei
•have the same chromosome number as original (parent) cell
MITOSIS & MEIOSIS, con’t.
Result of Meiosis:
•formation of 1 to 4 daughter nuclei
•have half the chromosome number as original (parent) cell
Concludes with cytokinesis
•division of the cytoplasm and organelles
I. MITOSIS
A. Terminology
1. Chromatin
2. Chromosome
3. Diploid (46 or “2N” in humans)
4. Haploid (23 or “N” in humans)
5. Homologous chromosomes
6. Somatic cells
MITOSIS, con’t.
B. PHASES: arbitrarily assigned
1. INTERPHASE:
a. NO division. Cell appears to be “resting”
b. the metabolic phase of the cell
Interphase, continued …
c. Chromatin visible
d. Nucleus, nuclear membrane, nucleolus visible
e. Centrioles located at poles
f. Longest phase
1. ~96% of the cell’s life cycle
2. average of 23/24 hours
MITOSIS, con’t.
2. Prophase
a. Centrioles move to opposite poles of cell
b. Chromatin condenses into chromosomes
c. Nucleoli disappear
d. Spindle apparatus is organized
MITOSIS, con’t.: Prophase
e. Toward end of phase, nuclear membrane dissipates
f. Phase ends as spindle fibers attach to centromeres
g. Each chromosome now consists of two chromatids
MITOSIS, con’t.
3. Metaphase
a. Chromosomes arranged around equatorial plate
b. “Single file”
c. Two spindle fibers attached at each centromere
MITOSIS, con’t.: Metaphase
d. A relatively short phase
e. Chromosomes easily counted (KARYOTYPE)
f. Phase ends as chromatids separate
g. Centromere splits as DNA replication is completed
MITOSIS, con’t.
4. ANAPHASE
a. Begins as chromatids separate
b. Spindles move chromosomes to opposite poles
c. Polar spindles elongate cells
d. Phase ends when chromosomes have arrived at poles
MITOSIS, con’t.
5. Telophase
a. “Reverse” of prophase
b. Identical sister chromosomes have arrived at opposite poles
c. Nuclear membrane reassembles
d. Spindle apparatus dissipates
e. Nucleolus reassembles
MITOSIS, con’t.: Telophase
f. Chromosomes relax chromatin
g. Centrioles replicate
h. Each chromosome consists of a single complete strand of DNA
i. Phase ends when nuclear membrane is completely reassembled
MITOSIS, con’t. …
C. CYTOKINESIS
1. Begins during anaphase
2. Completed during telophase
3. Result: two daughter cells
a. Genetically identical to parent cell
b. Contain ~1/2 the cytoplasm, organelles
II. MEIOSIS:• A special case of mitosis
• Occurs during maturation of sex cells (gametes)
• Result: daughter nuclei receive one half the number of chromosomes of somatic cells
• Makes sexual reproduction possible
II. MEIOSIS, con’t.
A. Terminology
1. Haploid: having a single set of chromosomes per
individual or cell (N)
2. Diploid: having two full sets of chromosomes per individual or cell
(2N)
II. MEIOSIS, con’t.: Diploid
a. Usually find sexual reproduction in diploid organisms
b. Provides enormous adaptive advantages:
1. allows for population variations
2. Increases chances for survival
II. MEIOSIS, con’t.: Terminology
3. Homologous chromosomes:
a. Chromosomes that pair during meiosis
b. Have the same morphology
c. Contain genes governing the same characteristics
MEIOSIS, con’t.: Terminology
4. Allele: one of the two or more alternate forms of a
gene
a. dominant, recessive, co-dominant
b. examples:
B = Brown hair (dominant)
b = blonde hair (recessive)
c. Different alleles arise by mutations
MEIOSIS, con’t.: Terminology
5. Gene:
a. sequence of DNA nucleotides
b. unit of heredity transmitted in the chromosome
6. Chromosome: sequence of genes
II. MEIOSIS, con’t.: Terminology
7. One gene – One enzyme theory:
• A gene is that part of a DNA molecule responsible for the synthesis of one enzyme (polypeptide)
II. MEIOSIS, con’t.:
B. Phases of Meiosis1. Two “sets” of events
2. Same names as mitosis
3. Must indicate phase ‘I’ or ‘II’
I = Reductional DivisionII = Equational Division
II. MEIOSIS, con’t.:
C. Reductional Division
1. Interphase I: Like mitosis
2. Prophase I:
a. Long, complex
b. Three subdivisions
II. MEIOSIS, con’t.: Prophase I
1. Early: like mitosis2. Middle: important
a. homologs pair
b. crossing over occurs
c. exchange of genetic info
d. called “tetrads”
3. Late: like mitosis
II. MEIOSIS, con’t.:
3. Metaphase Ia. Similar to mitosisb. Homologous pairs alignc. One spindle
fiber/centromered. Ends as one of each pair
is pulled to opposite polese. NO DNA replication!!
II. MEIOSIS, con’t.:
4. Anaphase I
a. Similar to mitosis
b. Members of homologous pairs move to poles
c. Moved by spindle fibers
II. MEIOSIS, con’t.:
5. Telophase I
a. Nuclear membrane reorganizes
b. Chromosomes “relax”
6. Cytokinesis: may not occur
II. MEIOSIS, con’t.:
7. End result
a. Nuclei are haploid (N)
b. Chromosome number is reduced by one-half
II. MEIOSIS, con’t.:
D. Equational Division:
1. Interphase II
a. NO DNA replication!!
b. “Coffee break” for nuclei
c. May not occur
II. MEIOSIS, con’t.:
2. Prophase II
a. Chromosomes condense
b. Spindle apparatus forms
c. Two fibers/centromere
d. Membrane dissipates e. Like mitosis
II. MEIOSIS, con’t.:
3. Metaphase II
a. Like mitosis
b. Chromosomes on equator
c. Single file
d. Ends with centromere replication
II. MEIOSIS, con’t.:
5. Telophase II
a. Nuclear membranes
reorganize
b. Nucleolus reorganizes
c. Chromosomes relax
d. Centrioles replicate
e. Like mitosis
II. MEIOSIS, con’t.:
5. Cytokinesis occurs
6. Result:
a. Females: unequal division of cytoplasm
-one ovum, 3 polar bodies
b. Males: equal division of cytoplasm
-four spermatozoa
II. MEIOSIS, con’t.:
7. Cells produced are:
a. Different from parent cellb. Different from each otherc. Haploid