Alleles
Alleles are just variations of genes that occur in pairs. They also occur in different combinations and locations within chromosomes. One way to describe them is as ‘slider-switches’ that relate to a person’s physical characteristics such as their height, body type and the colour of their hair and eyes. Depending on what alleles you’ve got, you’ll have a different type of facial structure or a different skin tone.
In order to compare two sets of DNA, such as that of a prospective father and son, alleles are used as markers in many tests, especially paternity and maternity DNA tests. The word itself is based on a Greek phrase which means ‘each other’ and this is because alleles only exist in pairs.
Sometimes alleles of two different types are present and they co-exist in what is called co-dominance, so, for example if a little girl has a mother with grey eyes and a father with green eyes, she might be born with one green eye and one grey eye. Both traits would be inherited from her parents due to both alleles being present and they could share co-dominance.
This same co-dominance can also be illustrated by discussing blood types, because if the girl also had alleles for an ‘A’ blood type and a ‘C’ blood type, she could easily end up with an overall co-dominant blood type of: ‘AB’. Usually, however, alleles are dominant and expressed (you can see that someone looks of a specific ethnic persuasion), or recessive and unexpressed (you can’t tell that someone is, for example: half Black African, despite them having the alleles in their genetic code).
