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Asked by to Kevin, Judith, James, Hannah, Aoife on 6 Jan 2019. This question was also asked by .
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Kevin Daly answered on 6 Jan 2019:
Good question! You are right, everyone has their own unique genome – even identical twins probably have a few differences! When scientists talk about “the human genome”, they mean the sequence of A’s, T’s, G’s and C’s common to all humans – including the genetic changes unique to the human species, that our closest relatives don’t have. So when we completed the Human Genome Project, we generated *a* human genome (that was actually a mixture of a few different people), but helped us identify the genetic changes specific to humans, the order and location of genes in the human genome.
This is a simplification that scientists know they are making. In reality, there is no one definite sequences of A’s, T’s, G’s and C’s which perfectly reflects the human species (or any species). It’s actually a big problem in the field of genomics – studying lots of genomes at the same time – as the reference genome we use may not well reflect the diversity of the species. We’re actually moving towards something called “graph genomes” – a way of describing the sequence of A’s, T’s, G’s and C’s in a species, plus whatever genetic variation is there.
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Judith Sleeman answered on 6 Jan 2019:
The human genome is a sort of ‘average’ genome. The original human genome project took many years and cost billions. Technology has advanced so much now, though, that it’s reasonably quick and inexpensive to sequence someone’s unique genome. This is the basis of some of the ideas about ‘personalised medicine’ at the moment: trying to predict which patients will benefit from particular drugs and which won’t.
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Gemma commented on :
The human reference genome is the sequence that we compare individual’s genomes to to try to make sense of them. It is not a “right answer” or “perfect” genome though, and there have been many versions of it over the years as we’ve filled in various gaps and improved it. It comes from a group of individuals who were sequenced as part of the Human Genome Project and then bits of their genomes were pieced together to give a whole genome sequence. This genome sequence doesn’t exist in a single person in the world as it is made up from a few people but most of the sequence comes from an African American individual though. When we sequence a person, we look to see what differences they have from the reference genome. We call these differences “variants”. We then try to make sense of the variants e.g. if a variant is very common in the population (even though it differs from the reference genome) we know that it can’t be harmful.