Feeds

Geneticists report 'semi-identical' twins

Egg and sperm three-way

The smart choice: opportunity from uncertainty

Geneticists in the US have discovered a previously unknown kind of twins they have called semi-identical. The twins are identical on their mother's side, but only share half of their father's DNA.

The discovery, which has been published in the journal Nature, has prompted some to suggest that the current classification system for twins is too simple and needs to be revisited.

The twins are technically chimeras: that is, their cells are not genetically uniform. Some cells contain male cells with an X and Y chromosome, others have female cells bearing a double load of Xs. In the journal Human Genetics, the researchers report that the proportion of XY and XX cells varies depending on the kind of tissue being examined.

For the genes to be distributed in this way, two sperm cells must have fertilised a single egg. Some DNA from each sperm is present in each child.

The sequence of events needed for the children to have been born is extremely unlikely: some scientists suggest the pair may be unique.

First, two sperm must fertilise a single egg. This does happen in about one percent of human conceptions. More often than not the fertilised egg does not form a viable embryo. This embryo must then split to form twins, who if they are to be identified as semi-identical, must subsequently come to the attention of scientists.

In this case, one of the twins was born with "ambiguous" genitalia, which brought in the scientists. They discovered that the baby is a true hermaphrodite, with both testicular and ovarian tissue, while the other twin is anatomically male.

Both children, now toddlers, are reportedly growing normally and have no mental developmental abnormalities.

According to Nature.com, in 2003 biologist Michael Golubovsky predicted that this kind of intermediate twin could result from "double fertilisation". He told the news service: There are a lot of unclear situations in the genetics of twins and twinning. We need to keep our eyes open for other unusual scenarios." ®

The Power of One Infographic

More from The Register

next story
World Solar Challenge contender claims new speed record
One charge sees Sunswift travel 500kms at over 100 km/h
SMELL YOU LATER, LOSERS – Dumbo tells rats, dogs... humans
Junk in the trunk? That's what people have
The Sun took a day off last week and made NO sunspots
Someone needs to get that lazy star cooking again before things get cold around here
Boffins discuss AI space program at hush-hush IARPA confab
IBM, MIT, plenty of others invited to fill Uncle Sam's spy toolchest, but where's Google?
Bad back? Show some spine and stop popping paracetamol
Study finds common pain-killer doesn't reduce pain or shorten recovery
Forty-five years ago: FOOTPRINTS FOUND ON MOON
NASA won't be back any time soon, sadly
Jurassic squawk: Dinos were Earth's early FEATHERED friends
Boffins research: Ancient dinos may all have had 'potential' fluff
prev story

Whitepapers

Top three mobile application threats
Prevent sensitive data leakage over insecure channels or stolen mobile devices.
Implementing global e-invoicing with guaranteed legal certainty
Explaining the role local tax compliance plays in successful supply chain management and e-business and how leading global brands are addressing this.
Boost IT visibility and business value
How building a great service catalog relieves pressure points and demonstrates the value of IT service management.
Designing a Defense for Mobile Applications
Learn about the various considerations for defending mobile applications - from the application architecture itself to the myriad testing technologies.
Build a business case: developing custom apps
Learn how to maximize the value of custom applications by accelerating and simplifying their development.