The human genome contains more than 20,000 protein-coding genes, which carry the instructions for proteins essential to the structure and function of our cells, tissues and organs. Some of these genes are very similar to each other because, as the genomes of humans and other mammals evolve, glitches in DNA replication sometimes result in extra copies of a gene being made. Those duplicates can be passed along to subsequent generations and, on very rare occasions, usually at a much later point in time, acquire additional modifications that may enable them to serve new biological functions. By starting with a protein shape that has already been fine-tuned for one function, evolution can produce a new function more rapidly than starting from scratch.
Pretty cool! But it leads to a question that’s long perplexed evolutionary biologists: Why don’t duplicate genes vanish from the gene pool almost as soon as they appear? After all, instantly doubling the amount of protein produced in an organism is usually a recipe for disaster—just think what might happen to a human baby born with twice as much insulin or clotting factor as normal. At the very least, duplicate genes should be unnecessary and therefore vulnerable to being degraded into functionless pseudogenes as new mutations arise over time
An NIH-supported team offers a possible answer to this question in a study published in the journal Science. Based on their analysis of duplicate gene pairs in the human and mouse genomes, the researchers suggest that extra genes persist in the genome because of rapid changes in gene activity. Instead of the original gene producing 100 percent of a protein in the body, the gene duo quickly divvies up the job . For instance, the original gene might produce roughly 50 percent and its duplicate the other 50 percent. Most importantly, organisms find the right balance and the duplicate genes can easily survive to be passed along to their offspring, providing fodder for continued evolution.
Caption: Whole genome sequencing revealed that sisters Addison and Trinity Hanners, ages 7 and 10, shown here with their mother Hanna, have a rare syndrome caused by a mutation in the MAGEL2 gene. Credit: Courtesy of the Hanners family
At the time that we completed a draft of the 3 billion letters of the human genome about a decade ago, it would have cost about $100 million to sequence a second human genome. Today, thanks to advances in DNA sequencing technology, it will soon be possible to sequence your genome or mine for $1,000 or less. All of this progress has made genome sequencing a far more realistic clinical option to consider for people, especially children, who suffer from baffling disorders that can’t be precisely diagnosed by other medical tests.
While researchers are still in the process of evaluating genome sequencing for routine clinical use, and data analysis continues to be a major challenge, one area of considerable promise centers on neurodevelopmental disorders. Such disorders—which affect about 3 percent of children—range from relatively common conditions like autism spectrum disorder to very rare conditions that impair the development of the brain or central nervous system. In the latest study, an NIH-funded research team reports that sequencing either a patient’s whole genome or whole exome (the 1.5 percent of the genome that encodes proteins) appears to be an effective—as well as a cost-effective—strategy for diagnosing neurodevelopmental disorders that have eluded diagnosis through standard means.
As most of you probably know, the human genome—our genetic instruction book—contains about 3 billion base pairs of DNA. But here’s a less well-known fact: if you would take the DNA from the nucleus of just one human cell and stretch it end-to-end, it would measure about 6 1/2 feet. How can a molecule of that length be packed into a cell nucleus that measures less than .00024 of an inch? Well, this fun video, which accompanies exciting new findings published in the journal Cell, serves to answer that fundamental question.
I’m proud to say that NIH helped to support the highly creative team of researchers that, over the course of the past five years, have mapped with unprecedented detail and precision how the human genome folds inside the cell’s nucleus. Among the many things they’ve learned is that, in much the same way that origami artists can craft a vast array of paper creatures using two simple folds, the genome is able to work its biological magic with just a few basic folds—including the all-important 3D loop
Credit: Jane Ades, National Human Genome Research Institute, NIH
Just this year, we’ve reached the point where we can sequence an entire human genome for less than $1,000. That’s great news—and rather astounding, since the first human genome sequence (finished in 2003) cost an estimated $400,000,000! Does that mean we’ll be able to use each person’s unique genetic blueprint to guide his or her health care from cradle to grave? Maybe eventually, but it’s not quite as simple as it sounds.
Before we can use your genome to develop more personalized strategies for detecting, treating, and preventing disease, we need to be able to interpret the many variations that make your genome distinct from everybody else’s. While most of these variations are neither bad nor good, some raise the risk of particular diseases, and others serve to lower the risk. How do we figure out which is which?
Jay Shendure, an associate professor at the University of Washington in Seattle, has an audacious plan to figure this out, which is why he is among the 2013 recipients of the NIH Director’s Pioneer Award.