American scientists have for the first time unlocked the genetic code of an entire family, and made a startling discovery - parents pass on fewer mutations than previously thought.
Scientists had long believed that each parent passed on some 75 genetic mutations to their children.
But the result of research by a team at the Institute for Systems Biology in Seattle and the University of Utah found this was nowhere near the case, according to their study published in Science Express.
In fact, after studying the genetic sequencing of an entire family - mother, father, daughter and son - researchers estimate that each parent passes on 30 mutations for a total of 60 to their children.
The results of the research could open the door to new studies into ways to narrow down the causes of some common diseases.
Most mutations are believed to have no effect on a child's health.
But knowing the rate at which parents give mutations to their kids is critical information, says Professor Lynn Jorde of the Department of Human Genetics at Utah.
"The mutation rate is our clock, and every time it ticks we have a new genetic variant," he says. "We need to know how fast the clock ticks."
The team even managed to pinpoint with astonishing accuracy where parental chromosomes crossed with their children's to create a new genetic trait.
The family whose genetic sequencing was unlocked was chosen because their children both suffer from an extremely rare combination of diseases.
Although the parents have no genetic abnormalities, they each carry recessive genes that led to their son and daughter being born with both Miller syndrome and Primary Ciliary Dyskinesia (PCD).
Only two families in the world have been diagnosed with Miller's syndrome, a disorder which leads to face and limb malformations. It is thought to occur in perhaps one in one million people.
And PCD is a disease in which the tiny hair-like structures in the lungs that are supposed to move mucus out of airways fail to function.
The chances of having PCD are estimated at one in 10,000. The odds of developing both PCD and Miller's syndrome are less than one in 10 billion, according to Jorde.
By comparing the genetic mutations in the two children with the Human Genome Project and other data banks, the researchers confirmed that four mutant genes are responsible for each illness.
Human beings have about 22,000 genes containing the genetic blueprint for human life. This blueprint, called DNA, comprises more than three billion base pairs that determine genetic makeup.