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Definition of Terms
gene - basic unit of heredity; codes for a specific trait
locus - the specific location of a gene on a chromosome(locus - plural loci)
genome - the total hereditary endowment of DNA of a
cell or organism
somatic cell - all body cells except reproductive cells
gamete - reproductive cells (i.e. sperm & eggs)
chromosome - elongate cellular structure composed of DNA and protein - they are the vehicles which carryDNA in cells
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diploid (2n) - cellular condition where eachchromosome type is represented by two homologous
chromosomes
haploid (n) - cellular condition where eachchromosome type is represented by only onechromosome
homologous chromosome - chromosome of thesame size and shape which carry the same type of genes
chromatid - one of two duplicated chromosomesconnected at the centromere
centromere - region of chromosome wheremicrotubules attach during mitosis and meiosis
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- sequence of phases in the life cycle of the cell
- the period from the beginning of one cell division to
the beginning of the next cell divisionTwo main parts
1. growth and preparation (interphase)
2. cell divisionA. mitosis (nuclear division)
B. cytokinesis (cytoplasm division).
Cell Cycle
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Cell Division
- the distribution of identical geneticmaterial, DNA, to two daughters cells
- functions in Reproduction, Growth and Repair
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State Phase Abbreviation Description
quiescent/
senescent Gap 0 G0 Resting phase
Interphase
Gap 1 G1
period of activity
characterized be
growth and
development
Synthesis S
DNA
replication occur
s during this
phase.
Gap 2 G2
cell synthesizes
organelles and
other materials
Cell division Mitosis M
Cell growth stops
at this stage and
cellular energy is
focused on the
orderly division
into twodaughter cells.
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C
hromosome structure
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nterphase -T
he cell is engaged in metabolic activity andperforming its prepare for mitosis. Chromosomes are not clearlydiscerned in the nucleus, although a dark spot called thenucleolus may be visible. The cell may contain a pair of centrioles (or microtubule organizing centers in plants) both of
which are organizational sites for microtubules
PHASESOF MITOSIS
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Prophase: The chromatin, diffused in interphase,condenses into chromosomes. Each chromosome hasduplicated and now consists of two sister chromatids. Atthe end of prophase, the nuclear envelope breaks down intovesicles.
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Metaphase: The chromosomes align at the equatorial plateand are held in place by microtubules attached to themitotic spindle and to part of the centromere.
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Anaphase: The centromeres divide. Sister chromatidsseparate and move toward the corresponding poles.
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Telophase: Daughter chromosomes arrive at the poles andthe microtubules disappear. The condensed chromatinexpands and the nuclear envelope reappears. The cytoplasmdivides, the cell membrane pinches inward ultimately
producing two daughter cells (phase:
Cytokinesis).
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-type of cell division by which germ cells (eggsand sperm) are produced
- process that reduces the number of chromosomes by half, so that the daughtercells are haploid (n)
- Comprise of two successive nuclear divisions
with only one round of DNA replication
MEIOSIS
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STAGESOF MEIOSIS
I.Interphase: Before meiosis begins, genetic material is
duplicated.
II. Meiosis 1
Prophase 1:
Duplicated chromatin condenses.Each chromosome consists of
two, closely associated sister
chromatids. Crossing-over can
occur during the latter part of
this stage.
(Micrograph showing condensed chromosomes in blue and the mitotic spindle in green
during prometaphase of mitosis)
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Metaphase 1:
Homologous chromosomes
align at the equatorial plate.
Anaphase 1: Homologous
pairs separate withsister chromatids
remaining together.
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Telophase 1:
Two daughter cells
are formed with each
daughter containing
only one chromosome
of the homologous pair.
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III. Meiosis 2: Gamete formation
Prophase 2: DNA does not replicate.
Metaphase 2: Chromosomes align at the equatorialplate.
Anaphase 2: Centromeres divide and sister
chromatids migrate separately to each pole.
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Telophase 2: Cell division is complete. Four haploiddaughter cells are obtained
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OOGENESIS
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CHECKPOINTSTO ENSURE FIDELITY OF CELL DIVISION
1. G1/S monitors the size of the cell and whether theDNA have been damaged
2.G2/M checkpoint controls the physiological
conditions in the cell prior entering to mitosis,especially DNA replication
3. M checkpoint monitors the formation of spindlefibers to the kinetochores associated with the
centromere
If the regulation of the cell cycle was not met in somecases this may lead to tumor formation.
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Amitosis
-the direct method of cell division characterized bysimple division of the nucleus without formation of chromosomes
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