By: Prof Ntsibande

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: 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.

Ovarian cancer cells dividing

STUDY HARD!!!!