Genetics

Different versions of the same gene found on a pair of chromosomes in the nucleus of a cell are called alleles. These can determine features such as eye color. Mendel recognized that there were dominant and recessive forms of these alleles. He also realized that genes are passed on from both parents and that recombination of genes during fertilization is a random event. This means that every person on the Earth (other than identical twins who came from the same egg cell) has a unique set of genes. This can be analyzed to provide a genetic fingerprint which looks a bit like a bar code!

It is important to know the relationship of chromosomes and genes. Chromosomes are made from long strands of DNA (deoxyribonucleic acid). Genes are small sections of the chromosomes. But what exactly do genes do? In short, they are 'instructions' for making proteins. Some of them make structural proteins whilst others make enzymes, which are very complex protein molecules that act as catalysts for many chemical reactions in the body.

Certain diseases are caused by the inheritance of faulty genes that are passed on to offspring from their parents. Two of the ones that are usually used in exam questions are cyctic fibrosis and Huntington's disease. When one or both of the parents are carriers of the faulty gene, genetics can show how likely it will be that their children will have the disease.

Do you know the difference between genes, chromosomes and DNA? Were you aware that your gender is an inheritance from your father - even if you are female? Try this quiz and refresh your memory on the subject of genetics.