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Genes (alleles)
are made of a chemical called DNA. This is the short way of writing
a long, complicated name - deoxyribonucleic acid. Molecules of DNA are
in the shape of ladders and in different genes the 'rungs' of the ladders
can be in a different order. There are millions and millions of different
ways the rungs can be arranged and so there are a very large number of
different alleles. This is what makes us all different from each other.
Genes contain
the instructions for building proteins. Proteins are chemicals which make
up many of the structural parts of the body, for example hair and muscle.
There are also proteins that are enzymes and they carry out chemical reactions
in different parts of the body.
Useful Links:
http://www.ch.ic.ac.uk/rzepa/mim/life/life.html
http://www.chm.bris.ac.uk/motm/dna/dnaj.htm
http://orion1.paisley.ac.uk/courses/stfunmac/glossary/DNAmol.html