The sexual evolution roles differ

Press, 25 August 1988, Page 21

The sexual evolution roles differ

Research on “virgin births” has shattered the theory that parents’ genes piay equal roles in children’s growth, writes ROBIN McKIE, science correspondent for the

“Observer.”

One of science’s most cherished laws — which says parents’ genes play absolutely equal roles in their children’s development — has been disproved. The discovery, by British researcher Dr Azim Surani, has overturned an idea that has gone unchallenged since Gregor Mendel laid down the laws of genetics a century ago. Dr Surani, of the Institute of Animal Physiology at Babraham, near Cambridge, has found that many of our genes actually “remember” throughout our lives whether they came from our mothers or fathers.

Previously a gene’s source — maternal or paternal — was thought to be unimportant. But now Dr Surani has shown that an embryo cannot survive unless it inherits a certain set of genes from one parent, and a certain set from the other.

“In particular, genes from the father are crucial to the development of the placenta, Which surrounds and nourishes the unborn child, while those from the mother are vital to the successful growth of the embryo itself,” he said.

Scientists are still coming to terms with the discovery, and believe it has profound implications.

It may explain why genetic diseases, such as Huntington’s chorea, and some forms of diabetes and muscular dystrophy, start at different ages in victims. This may depend on which parent passed on the defective gene.

The discovery may also affect agriculture, by showing that in some cattle breeds a desire characteristic, such as high-quality meat, may be only inherited through one line, either male or female. Dr Surani made his breakthrough while investigating “virgin births.” This phenomenon occurs in frogs and other amphibians when a female’s unfertilised eggs are prodded with a needle. This stimulation triggers embryonic development until a tadpole, containing . only, its mother’s genes, is produced. To find out why such virgin births are unknown in mammals, Dr Surani began experimenting on mouse embryos. He removed the father’s set of genes from a new embryo, and put in genes from a female. A huge embryo with virtually no placenta developed. But when two sets of male genes were inserted into an embryo, it failed to develop, although a very large placenta was produced. In neither case did the embryo

survive, showing that genes from both parents are vital to the survival of mammalian offspring. Dr Surani, in conjunction with researchers at the Ludwig Institute for Cancer Research in Montreal, has since used pieces of genetic material as tracers to show that up to a fifth of our genes may "remember” their parental sources in this way. Dr Surani calls these “imprinted” genes. .

“The discovery was quite a shock,” he said. “We just didn’t expect to uncover such a new, fundamental phenomenon.”

Scientists have not been slow to consider the discovery’s philosophical implications. “At the end of the day, a child is still an equal product of maternal and paternal genes. However, it is now clear that some particular genes from the mother, and some from the father, must be present,” said Dr Surani. “Now that may seem strange in the case of the placenta which one might expect to be a more ‘suitable’ role for a mother’s genes.” The explanation, he said, lies with the different roles that male and female mammals, including men and women, play during evolution. “It appears that a female’s genes are very conservative, and difficult to alter. They conserve the essence of a species, while the male’s genes are more plastic and pliable and take on changes and alterations. “Some of these changes or mutations have been failures, while some, like the development of the placenta, have been successes and have been incor-, porated in a new species.

“In other words, for the first time, we are now seeing evidence that male and female mammals, including men and women, play different roles during evolution.”