Miss Cybil N. Khumalo
University of Johannesburg
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 and Y chromosomes:
THE PHASES OF THE CELL CYCLE
The cell cycle includes the following phases:
Interphase (include G1- , S- [DNA synthesis] and G2
The result is 2 identical cells.
Why is Mitosis
Allow an organism to
Replace dead cells/tissue.
Reproduction in some
Where does Mitosis take place?
In all somatic cells (include all body cells and
excludes the sex cells – sperm/egg cells)
The process of Mitosis.
CONSIST OF A FEW PHASES:
Cell builds up enough energy for division
DNA replication occurs
Cell look normal, like before division
Nuclear envelope and nucleolus
Chromatin become more tightly
coiled, and condenses into
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
Daughter chromosomes move to
EARLY TELOPHASE – KARYOKINESIS
(DIVISION OF NUCLEUS
Daughter chromosomes reach poles.
Nuclear envelope surrounds
Nucleolus reappear at each pole.
Chromosomes become less condense
Two identical nuclei has been formed
LATE TELOPHASE – CYTOKINESIS
(DIVISION OF THE CYTOPLASM)
Invagination of the cytoplasm and plasma
membrane occurs. (Cleavage furrow forms in
animal cells and a cytoplasmic plate forms in
Continues until the cell in divided into 2 separate
cells. (Identical to one another and to the original
Cancer is caused by the loss of cell cycle controls in
Cancer cells usually continue to divide well beyond a
single layer, forming a clump of overlapping cells called
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.
(information from Campbell & Reece, Biology: 2010)
Ovarian cancer cells