Population amd Disease Genetics Group Centre for Population Health Sciences
College of this that and the other

Homozygosity

“Runs of homozygosity” or ROH are regions of the genome where the copies inherited from our parents are identical. This creates a run of homozygous variants, from tens of thousands to millions of letters in length. The two DNA copies are identical because our parents have inherited them from a common ancestor at some point in the past, recently in the case of a cousin marriage, but in fact we all carry ROH, because going far enough back in time we are all related.

The distribution of ROH records information about this history of intermarriage or isolation and consanguinity among our ancestors, but may also be important medically. This is because they allow certain variants, called recessive variants to be expressed. Recessive variants only have their effect when present on both copies of an individual’s genome, for example in a run of homozygosity. Recessive variants cause many genetic diseases such as cystic fibrosis, phenylketonuria and Tay-Sachs disease, hence the pattern of homozygosity is an important risk factor for these rare genetic conditions. We are interested in whether genome wide homozygosity is also a risk factor for common complex diseases like diabetes and heart disease.

Our recently published studies developed a genomic inbreeding coefficient, and shown its relation to population history; and carried out the first global survey of ROH. Analysis of ROH in a first generation African x European individual, as featured in the Channel 4 documentary Is it better to be mixed race?, revealed a remarkable lack of ROH compared to all other samples tested. This is presumably because his parents have very little shared ancestry over the thousands of years.

 

 


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