Question: All humans are so different, how can you have a 'normal' genome?

Chris Kettle answered on 15 Jun 2012:

Nice question!

Its true that there isn’t just one “normal” genome, there are millions, each with slightely different changes. Its just whether those changes are significant enough to have a clinical effect and become abnormal.

Its also a question of scale. Looking down the microscope the patients chromsomes can look normal, 46,XY for a male and 46,XX for a female. But they could have a submicroscopic change (we can see 5 million base pair changes using the microscope) – for example a single base pair deletion in a gene that causes it to stop working. This would be abnormal and yet appear as a normal genome at the microscope level.

Imagine if the government were doing a survey of which roads needed repairing in the UK. If they took the picture from space and tried to look at the entire Uk at once they would think that the roads were fine. Now if they get in a helicopter and fly around they will see problems on the major roads. If they then drive around the actual roads they will see all of the problems.

WHich is quickest to do? It would take a lifetime to walk/drive all of the UK roads checking them for any problems and yet its one photograph to check the entire UK. Unfortunately, its a balance between how much you can see and the time it takes.

In future, when everyone has their genome sequenced then normal will come to mean not significantly/clinically abnormal due to the huge variation between people.

Hope that answers your question – very good question though.