Susumu Ohno’s “Junk DNA”

Historians are frequently enchanted by things discarded as useless by the general public. But I think anyone interested in evolution would find the study of non-gene coding DNA fascinating, including the scientist featured here. This is Susumu Ohno, one of the United States’ foremost geneticists and evolutionary biologists, and he came up with the term “Junk DNA”.

Susumu Ohno (1928-2000) studied genes before modern sequencing tools arose. Considering we humans have 3 billion base pairs of DNA, that was no small task. As scientists now recognize, only a small percent of that material actually codes for genes. Some of those base pairs we humans need to give direction to our cellular growth: this DNA turns stem cells into body parts, or triggers the release of hormones that make life possible. But some of this material, Ohno realized, was “junk”: base pairs that exist as a sort of record of our evolutionary history.

In our DNA lies the story of the animals we evolved from — coding sequences that we don’t use, but that match other animals and show our common ancestry. The yolk sac genetic sequence is an example — we humans obviously do not lay eggs like birds and reptiles outside our bodies, but we share with these animals the DNA to make such an organ with protein-rich food for embryos to use as they develop in their eggs. As embryos, we even grow a small yolk sac in the earliest weeks, which eventually dissipates by the fourth week as the placenta forms. (See second photo.)

Susumu Ohno contributed enormously to our understanding of evolutionary development, particularly in discovering the ways gene duplication contributes to change in species. He was also an artist, and composed music by translating genes into notes, making pieces that we can listen to today.