Genes and behavior
Even though identical twins come from the same genetic material, they turn out to be very different people looking alike. So different that one of the twins could get a genetic disorder at the age of 40 and the other could be the most fit person! Why is that so?
The interplay of genes and the environment influences behavior. But highly evolved animals, like humans, depend only on a small fraction of the nature-vs-nurture characteristics of genes. Mostly, human behaviors are influenced by the innate properties of genes. Genes achieve this through RNA (transcription of genes) and proteins (translation of mRNA). In this way, genes assemble developmental programs that allow cells to have a particular property and carry out specific functions. Genes are stably inherited over several generations where their processes also involve new experiences shaping their function.
Even though such genes are very similar in identical twins, the difference lies in how genes interact with smaller molecules ( such as proteins) within a particular cell type to activate/deactivate gene expression. This creates a specific pattern of gene expression in a particular cell type serving its specific function. This is called epigenetics.
Epigenetic changes can either enhance or decrease the expression of specific genes by interfering in their transcription process. Such interference happens through chemical tags that are attached to the DNA or the small molecules that interact with the DNA. These chemical tags could be methyl, phosphate, or acetyl groups. These chemical tags attached to the genome in a given cell are called Epigenome. In the case of the methyl group, it often inhibits the gene expression by interfering with the transcription process or by causing tight coiling of that fragment of the DNA making it more inaccessible (heterochromatin). Whereas some chemical tags enhance the gene expression by allowing that particular part of coiled DNA fragment to unwind so that its available for transcription (euchromatin).
Such epigenetic changes are conserved across several generations. The on and off characteristic of an epigenome can be influenced by external environment such as life-style, chemical exposure, and medication. This is where nature-vs-nurture kicks in. Environmentally influenced epigenetic changes could lead to genetic disorders such as schizophrenia or could lead to cancer by switching-off tumor suppressing protein.
Humans have 200 cell types. Even though all the cells have the same genome, epigenetics results in different cell types and their specific function. Epigenetics is the answer to the question of why twins are so different even though they are so alike at the genome level. As we get older, including twins, our epigenome undergoes changes that make us unique and are also passed on to the future generation. Childhood experiences and adult choices could potentially change the epigenome and shape the lives of one’s offspring. A balanced lifestyle, exercise, and lesser exposure to contaminants will maintain a healthy epigenome. Scientists have realized the potential of epigenetics and are trying to manipulate it via gene-editing techniques to treat several disorders.