It’s one thing to say our parents are bananas, another to say they are literally a banana.

From what you learned in high school, you might remember genes and DNA as sort of the same thing. DNA is the blueprint of complex life. Every cell of ours contains the same DNA blueprint. This is why a small sample of a persons hair, skin, or blood can be used to identify a suspect at a crime scene. Unfolded, this DNA is 6 feet long and 30,000 times thinner than a strand of hair.

You might also remember that DNA contains 4 basic ‘letters’ — Adenine, Thymine, Guanine, Cytosine. These form ‘words’ that are 3 letters long and each word codes for a building block of a protein. These words form a ‘sentence’ called a gene, and each sentence codes for a protein. Proteins are essential for organisms and participate in virtually every process within cells. But is that all DNA is composed of — genes that code for proteins?

Turns out, genes are a small fraction of DNA. Only 1-2% of DNA is composed of genes. Around 8% consists of gene regulatory regions. This 8% controls when genes are turned on and off.

These control regulatory activities such as promotion of transcription (the process of transcribing a DNA to an RNA molecule, serving ultimately as a template for protein synthesis), enhancement, and finally — silencing of gene expression.

The rest 90% is called a variety of things — from junk DNA to dead and unknown DNA. We really don’t know what most of our DNA is used for!

A composition | Skanda Vivek

The importance of this unknown DNA is a contentious debate. The term junk DNA was originally coined in the early 1970s. In fact, a nature review co-authored by nobel prize winner and co-discoverer of DNA Francis Crick states:

“there is a large amount of evidence which suggests, but does not prove, that much DNA in higher organisms is little better than junk. We shall assume, for the rest of this article, that this hypothesis is true.”

In recent times, there have been various explanations as to what exactly is the use of this large seemingly irrelevant chunk of DNA. In 2012, a research program called the ENCODE project reported that more than 3/4th of DNA non-coding elements were transcribed. This led them to conclude that over 80% of DNA is functional.

However, this has been widely criticized by scientists. The argument comes down to whether or not transcription implies biochemical functionality. Just because something is replicated in the body, does not imply its usefulness. The large consensus is that this junk DNA does not carry evolutionary advantage.

Now lets come back to the parent — banana question posed in the beginning. Humans and bananas share around 50% of genes — which code for proteins. That comes out to be 0.5–1% of our DNA.

Whereas we share 50% of DNA with each parent. That might offer some relief. Except that genes code for proteins, which means bananas and humans share much of the proteins! So basically, a lot of what we do to stay alive is similar to what a banana does, at least qualitatively from the similarity in protein products.

But here’s where things get interesting. In an interview with Scientific American, chief ENCODE scientist Ewan Birney stated that while humans and mice have extremely similar genes, their regulatory mechanisms are quite different. And there is more complex regulation of genes as well as rapid evolution of regulatory elements in humans as compared to mice.

Its a tantalizing thought — that many differences between humans, bananas, and mice might come down to the regulation of proteins, and not the proteins themselves.