Magazine article Science News

New Evidence Supports Genomic Imprinting

Magazine article Science News

New Evidence Supports Genomic Imprinting

Article excerpt

New evidence supports genomic imprinting

In a mid-19th-century monastery garden, Gregor Mendel's experiments with smooth and wrinkled peas revealed the rules by which parents pass on traits to their offspring. But a theory called genomic imprinting is putting a new wrinkle into Mendelian genetics: A gene's expression may depend on which parent contributed in (SN: 5/20/89, p.312).

In the latest finding, Susan Malcolm of the Institute of Child Health in London and her colleagues report in the March 23 LANCET on two children who developed a rare type of mental retardation called Angelman's syndrome. Because of an error during sperm formation, each child inherited two chromosome 15 segments from the father and none from the mother, a rare condition called uniparental paternal disomy. According to Mendelian genetics, neither child should have suffered ill effects because each got a normal and complete set of genetic material, albeit from only one parent.

The British report parallels a finding by Robert D. Nicholls and other researchers at the Children's Hospital in Boston that a double dose of maternal chromosome 15 leads to a clinically different form of mental retardation called Pradel-Willi syndrome (SN: 11/18/89, p.324).

The results of these two studies strongly support genomic imprinting in humans, Malcolm says, because they show that the same gene has different effects depending on its parental origin.

"Clearly, for this bit of chromosome 15 [to function properly], you just have to have a contribution from mother and a contribution from father--which Mendel didn't know about," Malcolm told SCIENCE NEWS.

Researchers suspected the influence of genomic imprinting in the two syndromes because each had an odd inheritance pattern. Using DNA probing techniques developed in this 1980's, geneticists had discovered that about half of Angelman's cases were missing genetic material from a portion of the mother's chromosome 15 and about 60 percent of Pradel-Willi cases were missing material from the father's chromosome 15. …

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