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 Chromosomes form when the chromatin network in the
nucleus of the cell, coil up, shortens and thickens.
 Each organism has a specific amount of chromosomes.
 All humans have 46 chromosomes.
 These chromosomes are arranged in identical pairs
called homologous chromosome pairs –
 Therefore humans have 23 homologous pairs of
chromosomes.
 These chromosomes is only visible during cell division
processes.
 One chromosome consist of 2 chromatids and one
centromere that attach the chromatids together.
 Each chromatid consist of genes which in turn consist of
DNA.

X andY chromosomes:
gonosomes/sex-chromosomes
Colored bands
represents different
genes

The cell cycle includes the following phases:
 Interphase (include G1- , S- [DNA synthesis]
and G2 phase)
 Mitosis
 Cytokinesis
 Growth
The result is 2 identical cells.

 Allow an organism to
grow.
 Repairs damaged
cells/tissue.
 Replace dead cells/tissue.
 Reproduction in some
simple organisms.

 In all somatic cells (include all body cells and
excludes the sex cells – sperm/egg cells)

 CONSIST OF A FEW PHASES:
 INTERPHASE
 PROPHASE
 METAPHASE
 ANAPHASE
 TELOPHASE

 Cell builds up enough energy for division
process.
 DNA replication occurs
 Cell look normal, like before division

 Nuclear envelope and nucleolus
disappear.
 Chromatin become more tightly
coiled, and condenses into
individual chromosomes.
Chromosomes arrange randomly
in the cell.
 Centrioli move to opposite
poles, with spindle fibers
stretching between them.

 The centrioli reached the opposite poles with
the spindle fibers in between.
 The chromosomes arrange randomly on the
equator, each single chromosome attaching
to a separate spindle fiber by means of the
centromere.

 The spindle fibers pull tight.
 The centromers attaching the chromatids of
the chromosomes split in half.
 Daughter chromosomes move to opposite
poles.

 Daughter chromosomes reach
poles.
 Nuclear envelope surrounds
chromosomes.
 Nucleolus reappear at each pole.
 Chromosomes become less
condense forming chromatin.
 Two identical nuclei has been
formed

 Invagination of the cytoplasm and plasma
membrane occurs. (Cleavage furrow forms in
animal cells and a cytoplasmic plate forms in
plant cells)
 Continues until the cell in divided into 2
separate cells. (Identical to one another and
to the original cell)

 Cancer is caused by the loss of cell cycle controls
in cancer cells.
 Cancer cells usually continue to divide well
beyond a single layer, forming a clump of
overlapping cells called a tumor.
 Malignant tumors invade surrounding tissues and
can metastasize exporting cancer cells to other
parts of the body, where they may form secondary
tumors.
 They do not exhibit anchorage dependence or
density dependent inhibition.

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Mitosis(cell division)

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