When I was in school at MIT and Harvard in the 1980s and 1990s,
I was taught that there were 100,000 or so human genes, every
one encoding a protein. The properties of those genes were
unknown. Today, I teach that our genome contains only 21,000
protein-coding genes. To our surprise, there are thousands of
additional genes that don’t encode proteins. All of these genes
have been described in great detail. I was taught that the parts
of the genome not encoding proteins were “junk.” Today, we know
that this junk makes up three-quarters of our functional DNA.
Parts of it help exquisitely control where and when genes are
active in the body. I was taught that “genetic diseases,” such
as cystic fibrosis, are caused by mutation of a single gene,
with only a small handful of these mutations known. Today,
precise causes are known for 2,800 of these rare single-gene
disorders. I was taught nothing about the more complex genetics
of common diseases. Today, we are learning at dizzying speed
about the interplay of genes a