Biology revision
Chromosomes and genes
Chromosomes are genetic structures found in the nucleus of the cell. Humans have 46 chromosomes in each cell arranged in 23 pairs. Chromosomes are made up of smaller sections called genes, genes are made of short lengths of DNA (deoxyribose nucleic acid). Genes act like codes to control characteristics such as eye colour and hair colour.
A genome is an organism’s complete set of DNA. Each genome contains all the information needed to build and maintain that organism.
DNA has a structure known as the double helix. It is made of four bases and they always make the same pairs.
A and T
G and C
This is known as base pairing.
DNA is made up of three sub units they are:
· Phosphates
· Sugars
· Bases
Mutations
Mutations are random changes in the structure or numbers of chromosomes or genes.
Cancer
Cancer is uncontrolled cell division caused by damage (change) to the genes or chromosomes in a part of the body. Cancer is caused by mutations.
Skin cancer
To prevent skin cancer you should take the following precautions into consideration:
· Avoid mid-day sun and the early afternoon when sun is its strongest.
· Wear sun cream.
· Wear a hat to protect face and eyes.
· Do not spend long periods in the sun.
Gametes
Gametes are sex cells. The male gametes are the sperms, and the females gametes are the eggs.
Genetic conditions
Some medical conditions are caused by problems with chromosomes or genes. Two examples are down syndrome and cystic fibrosis.
Cystic fibrosis
Cystic fibrosis is an inherited disor...
