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Normal genetic variation

This step explains about single nucleotide polymorphisms (SNPs), normal variation within the human genome and their role in disease development.
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Genetic variation. We are all, as humans, very similar. Similar enough to be recognisable as humans. Much more similar than members of many other species are to each other. But still, we’re all different. Different hair, different skin, different abilities, different likes and dislikes. So different as to be unique. Even identical twins who originate from the same fertilised egg are now thought not to be as genetically similar as previously thought.
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In fact, no two individuals are exactly the same genomically. Why? Because of genetic variation. Genetic variation is a term used to describe the differences in the DNA sequence in each of our genomes.
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Although there are many different changes to the genetic architecture which drive variation, the commonest type of genetic variation is what we call a single nucleotide polymorphism, or a SNP. A SNP is the substitution of a single base or nucleotide with another base or nucleotide. They occur throughout the genome, on average about every 300 bases. And many SNPs are seen frequently within the general population.
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As technology and our understanding of the genome improves, we’re beginning to understand the importance of SNPs, although we still have a lot to learn. For instance, we know that genetic variation contributes to the evolution of species. Favourable characteristics are selected for, survive, and are passed on. This is what we call natural selection. In addition, we now know that some SNPs can predispose to the development of disease, whereas others can protect against disease. When the full set of detrimental and protective SNPs for a given disease are understood, we will be in a position to offer individuals SNP profiling to more accurately determine their risks for developing a given illness.
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We are also beginning to understand that the combination of SNPs that an individual has will determine how they respond to some medicines, such as warfarin. We will talk much more about this in week four. But ultimately, we are still far more alike than we are different. If visitors from another planet landed on Earth, they would have a hard time telling us all apart.
Watch this video to learn about single nucleotide polymorphisms (SNPs), normal variation within the human genome and how we are beginning to understand that SNPs have a key role in disease development and our response to medicines.

Talking point

In this video, we mention that identical twins are not exact genetic copies of each other. New laboratory genetic tests have the ability to correctly discriminate between identical twins.
Yet, identical twins originate from the same fertilised egg with the same genetic material. We will discuss the science behind this riddle in future steps, but please share any thoughts you have as to why this might be.
Image: © SGUL, A silhouette of human evolution created in Adobe Illustrator by Tkgd2007. Licensed under CC BY-SA 3.0
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The Genomics Era: the Future of Genetics in Medicine

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