Chromosomes form through coiling and condensing of chromatin during cell division. Humans have 23 pairs of homologous chromosomes, for a total of 46. Each chromosome contains DNA and genes. The cell cycle involves interphase and mitosis, resulting in two identical daughter cells through cytokinesis. Mitosis consists of prophase, metaphase, anaphase, and telophase where the chromosomes align and separate. Cancer occurs when cell cycle controls are lost, allowing uncontrolled cell division and tumor formation.

1. By: Prof Ntsibande

2.  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.

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

4. 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.

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

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

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

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

9.  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.

10.  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.

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

12.  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

13.  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)

15.  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.

16. Ovarian cancer cells
dividing

17.  STUDY HARD!!!!