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DNA is 99·9% identical among humans – all our variations of shape, size and color are within that remaining 0·1%
Why we are all unique
Each of us has a unique combination of genetics variants, including SNPs in our DNA
A SNP or “snip” can affect our inherited risk of disease
A SNP, pronounced “snip”, is a single variation in the nucleotide sequence of DNA and stands for Single Nucleotide Polymorphism that can affect our inherited risk and a multitude of other characteristics. Most of our features, internal and external are determined or influenced in some way by such variations in our DNA, i.e. by SNPs. Each of us is different because we carry a unique combination of genetic variants, including SNPs.
The slow rate of change to our DNA explains why children are so like their parents
SNPs are the result of alterations to DNA, usually called mutations
These mutations accumulate very gradually as DNA is passed on from parent to child, generation after generation. The slow rate of change to our DNA explains why children are so like their parents. However, the fact that our DNA can change, given enough time, explains why we are all different in size, shape, color and many other characteristics. Such differences are the result of the many SNPs that have arisen in the DNA of our species and its predecessors.
Even though the differences between people around us are often easy to see, it is nonetheless important to bear in mind that humans are on average 99.9% genetically identical. This means that if you were to compare your chromosomes with those of a random person, we would expect to find, on average, one SNP that differs every thousand DNA nucleotides. Our DNA is also surprisingly similar to that of other animals and organisms.
Our blood group and eye color are determined by which alleles we inherit
Alleles are different versions of the same gene
An allele is the version of a particular SNP or chromosome segment that you inherited from either your mother or father. Your cells carry 23 pairs of chromosomes, where one was inherited from your mother and the other from your father. This means that for any nucleotide or SNP located on an autosomal chromosome you have inherited two versions (one maternal and the other paternal). These are usually referred to as your two alleles for that particular location in the genome. For the vast majority of chromosome pairs, you will have inherited the same allele from both parents (for example, two copies of the cytosine nucleotide, represented by the letter C). A systematic examination of the nucleotide sequence of your 23 chromosome pairs would reveal millions of locations where the nucleotides you inherited from your parents were different (for example, a C allele from your mother and a T allele from your father).This content was last reviewed on February 18, 2010.
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