Cytogenetics is the study of chromosomes and how changes in chromosome structure and number affect the individual. In this video, Professor Porteous describes the process of hunting for the DISC1 gene, a gene disrupted by a balanced translocation on chromosome 1q42.

A tremendous advantage of having a family with a balanced translocation segregating with a common complex disease like this is that it allows us to pinpoint a precise region of the human genome to look at. Because there’s a very clear hypothesis here – that is that the translocation has disrupted a gene and that by disrupting a gene it has had a causal link to the development of the psychiatric illness and related symptoms in that family. Now usually when you go off gene hunting, it’s a hard task, even now, it’s hard now to track down a particular gene within a particular region of a chromosome that might be implicated by family studies. In this case, what we needed to do was to walk along chromosome 1 until we saw a change and we started to see the signature of chromosome 11 and that transition from chromosome 1 signature to chromosome 11 signature would tell us that we had identified the translocation breakpoint. Then we could look at the sequence surrounding the breakpoint and ask “what did we find?” And the answer was that we found evidence for a gene. But normally when you look at a gene sequence you can get a pretty good idea early on about what it’s related to – to other genes in the genome because genes fall into gene families. Not in this case, it was a unique gene, a gene that we’ve never seen before and that’s why we gave it the name disrupted in schizophrenia 1. And since we’ve discovered it in the year 2000, we’ve been working hard to try and work out what it does.

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