June 13, 2011

Parents Give Their Children 60 New Genome Mutations

Researchers have discovered that parents give their children about 60 new genome mutations.

The new value is reported in the first-ever direct study of new mutations coming from mother and father.

Researchers measured directly the number of mutations in two families, using whole genome sequences from the 1000 Genomes Project.  The results also reveal that human genomes, like all genomes, are changed by the forces of mutation.

New mutations are the ultimate source from which new variation is drawn. 

Professor Philip Awadalla, from the University of Montreal and co-leader for the project, said in a statement: "Today, we have been able to test previous theories through new developments in experimental technologies and our analytical algorithms. This has allowed us to find these new mutations, which are like very small needles in a very large haystack."

The team wrote that finding new mutations is extremely technically challenging because only 1 in every 100 million letters of DNA is altered each generation.

"We human geneticists have theorized that mutation rates might be different between the sexes or between people," Dr Matt Hurles, Senior Group Leader at the Wellcome Trust Sanger Institute, said in a statement. "We know now that, in some families, most mutations might arise from the mother, in others most will arise from the father.

"This is a surprise: many people expected that in all families most mutations would come from the father, due to the additional number of times that the genome needs to be copied to make a sperm, as opposed to an egg."

The findings come from a study of two families consisting of both parents and one child.  The researchers looked for new mutations present in the DNA from the children that were absent from the parents' genome.  They also looked at about 6000 possible mutations in the genome sequences.

The team sorted the mutations into those that occurred during the production of sperm or eggs of the parents and those that may have occurred during the life of a child. 

According to the findings, in one family, 92 percent of the mutations derived from the father, where as only 36 percent of the mutations derived from the father in the other family.

The number of mutations passed on from a parent to a child varied between parents by as much as tenfold. 

A person with a high natural mutation rate might be at greater risk of misdiagnosis of a genetic disease because the samples used for diagnosis might contain mutations that are not present in other cells in their body.

Reference: Conrad DF et al. (2011) Variation in genome-wide mutation rates within and between human families. Nature Genetics, published online 12 June 2011


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