Making Sense of Junk

Each cell in our body carries genetic material which is written in 4 different alphabets. In almost all cells of the body there are close to 6 billion such letters in the book of life. Six billion is actually duplicated information, one set from each parent.  Hence if we want to put non-duplicated info into a book it will take a book with 3000,000 pages if we can pack 1000 letters per page. Human genome project which sequenced the entire human genetic information told us that there are ~20,000 genes in human beings, which is less than 2% of the 3 billion nucleotides. What about the remaining 98%? Nobody really knows. To cover up the ignorance some called it the ‘Junk DNA’.

What would it take to make two people differ at the level of your DNA? Let’s say how much change is needed to make a brunette a blonde? The answer may surprise you. It indeed surprised me. All it takes is just one nucleotide change. i.e. if we change one letter in the three million-page book we talked about earlier the entire appearance of the book will change (yup, not the best analogy, I agree). Study published recently from Kingsley lab (Stanford) suggested just the same. They found a mutation in the genome (Single Nucleotide Polymorphism, SNP, which means a variation of genetic sequence that is present in more than 1% of the population).

Interestingly this variation is not present in any of the 20,000 or so genes we know about. But it lies in a part of the genome, which would be called ‘junk DNA’ few years back. It lies ~350kb away from a gene (if one nucleotide is 1 meter, it would be like turning on a light bulb with a switch located 350 km away). Technically this SNP lies in a region defined as ‘enhancers’ that are genomic regions that regulate a gene by long distance contacts. The full connection of this gene and blond hair is not fully characterized. There are more experimental validation needed for this link and also the underlying mechanism. It is quite possible that this SNP might have changed a network of genes or genomic interactions that might have bring about the observed phenotype. But even without going to the details, this study reminds us the complex, yet subtle ways through which body patterns and similar changes can happen in a population.