Hunting for a gene?
You have about 24,000 different genes, each made up of between a few hundred to a few thousand base pairs of DNA code. These genes are bundled up into 23 pairs of chromosomes, each of which carry thousands of different genes and is made up of millions of base pairs of DNA code.
Some genes cause genetic conditions when they are missing or altered. When scientists look at the chromosomes of someone with a genetic condition, they occasionally see bits of chromosomes missing: an important clue at the start of a gene hunt. Otherwise, they must use 'reference' fragments of DNA to track genes in affected families.
Can genes be found in families?
Researchers can track down genes involved in genetic conditions by looking at DNA from affected families. They study how the condition is passed on from one generation to the next, looking for a piece of DNA that is inherited along with the condition. During the search for the gene involved in Huntington's disease, for example, a DNA fragment from chromosome 4 gave researchers the clue they needed.
Where on the chromosome?
How much do your genes affect you?
Genes affect our susceptibility to several common illnesses, but so do many other things, like our diet, surroundings and lifestyle. It's a bit like betting on a horse race – the horse, rider, course and weather can all affect the outcome in a way that is hard to predict. Many genetic and non-genetic factors affect our health (and personality and appearance), but scientists don't yet know what they all are or how they interact. Ways of finding out include population studies and studies of twins.