What is a Phenotype?

Phenotype comes from Greek phainein, "to show." It describes the outward physical manifestations of your genes (or genotype) as well as the physical manifestations of any environmental influences on your life. It is anything that is part of the observable, structure, function or behaviour of a person.

For example the colour of your hair, your fingerprints, your blood type are all phenotypic expressions of the information on your genes. The fact that you wear your hair short, wrap around sunglasses and are phenotypic expressions of environmental influences.

A phenotype therefore is the outward expression of our internal genetic code.

It is the phenotype that people are usually referring to when they say that a baby "looks" like they have a certain Trisomy or other chromosomal anomaly. What they are saying is that the additional genetic material results in certain features that are more common amongst other children with the same syndrome. While a phenotype may give doctors some idea as to what condition the person has, it is not diagnostic as each person is a unique individual and the expression of the genes is different.

Below are groups of photographs of children who are effected by different Trisomy conditions. You can see from these photographs that while each child has the same anomaly they are very different yet there are also similarities. Unlike Trisomy 21 (Down Syndrome) the phenotype of the other Trisomies can be quite subtle.

In trisomy 18 some of the phenotypic features may include a small angular face, clenched hands, ptsosis, a small "rosebud" mouth, low set ears etc

	In trisomy 13 some of the phenotypic features may include a high, wide forehead, small eyes, broad nose etc.

Can you see the phenotypic features of Trisomy 9p?

Sometimes there are singular phenotypic features that are very characteristic of a syndrome.

On the left is a photograph of the characteristic hand posturing in Trisomy 18 and on the right you can see the curving of the little finger in Trisomy 9p.