Sperm analyzed, one by one
Close look at DNA reveals basic processes of sex cell
Some scientists really throw themselves into their research, but Stanford University biophysicist Stephen Quake has taken the all-in approach to a whole new level.
Using his sperm, Quake and colleagues compiled the first-ever genetic blueprint for a single sperm cell. The results shed new light on molecular processes such as mutation and recombination in humans, Quake and his colleagues report in the July 20 Cell.
Figuring out how often humans make mistakes in copying DNA so that single DNA units are changed, or mutated, is important for a variety of reasons, including figuring out how long ago humans diverged from other species, says Laure Ségurel, an evolutionary geneticist at the University of Chicago. “Every calculation is based on this mutation rate,” she says.
In past studies, scientists estimated this rate either by comparing human DNA with that of other species to see how many changes have occurred since that species split from humans, or by studying families to see where children have different DNA than their parents. By studying individual sperm cells, Quake and colleagues calculate the human mutation rate at 2 to 4 changes per 100 million DNA units per generation. That is higher than the rate calculated by looking at families (SN Online: 6/13/11), but consistent with evolutionary estimates.