B1.1 What are genes and how do they affect the way that organisms develop?
A GENE is a short section of DNA. Genes carry instructions that control how you develop and function – they are long molecules of a molecule called DNA. Each gene codes for a specific protein by specifying the order in which AMINO ACIDS must be joined together.
These proteins can be:
STRUCTURAL PROTEIN: Gives the body structure, rigidity and strength E.g. Skin, Hair, Muscles etc
FUNCTIONAL PROTEIN: Enables the body to function E.g. Enzymes, Antibodies etc.
The differences between individuals of the same species are described as VARIATIONS.
Variations may be due to:
- GENOTYPE – The genetic makeup of an organism. The different characteristics that an individual inherits, E.g. whether you have dimples or not.
- PHENOTYPE – The observable characteristics the organism has. How the environment changes an individual, E.g. cutting the skin may cause a scar.
IDENTICAL TWINS have the same set of genotype however any differences between them is because of environment.
CONTINOUS VARIATION shows when some characteristics are controlled by several genes working together e.g. eye colours and height. For instance it was originally believed that eye colour was due to a single gene. It is now known that there are a number of genes coding for different pigments in the iris, mainly on chromosome 15 in humans. This means that there is enormous variation in eye colour.