When we think about biological traits, we often associate them with genetics, mostly referring to the gene sequences within our genomes. The building material of our genome, the DNA, is composed of four nucleobases and a sugar backbone. The four bases make up what we call the genetic code. Three such bases in a row, called a codon, encode one of twenty amino acids. 4 out of the 64 possible codons signal the start or end of a protein coding sequence. But genetics is not all the information there is that influences our personal traits. There is literally another “layer” of information on top of the genetic code: Epigenetics. The Greek work “epi” meaning “on” refers to the chemical changes of the DNA or surrounding proteins that affect how the body can read genes. While genetics determine a protein’s sequence, epigenetics can change what proteins are synthesized, where, and at what time. As opposed to mutations within DNA sequences, epigenetic changes are reversible. Epigenetics are heritable but show dynamic plasticity in response to environmental cues. The changes are essential to normal and adaptive differentiation and development of organisms.

You must know the feeling of opening the box of a jigsaw puzzle, seeing all the pieces in front of you, knowing from the cover what the whole picture will look like, but not knowing where the individual pieces belong? You might have an idea that the blue pieces belong to the sky and the red pieces to the house, but you don't quite know the details. This is how researchers who sequence human genomes feel like when they analyze their sequencing data. With the latest technologies, they are able to sequence all the 3.2 billion bases of the human genome. The first milestone was the completion of the human genome project in 2003. From these 3.2 billion bases, researchers could deduce around 20000 genes making up only less than 2% of the genome — a surprising finding since it left more than 98% of the sequences without any obvious function.