Rare twins discovered in America
Jun 20, 2007
WONDERS never end! Scientists have revealed details of the world’s only known case of “semi-identical†twins.Born in the US, the twins, who were conceived normally, only came to the attention of scientists because one was born a hermaphrodite, with both ovarian and testicular tissue, while the
Grain of Science
WONDERS never end! Scientists have revealed details of the world’s only known case of “semi-identical†twins.Born in the US, the twins, who were conceived normally, only came to the attention of scientists because one was born a hermaphrodite, with both ovarian and testicular tissue, while the other child is anatomically male.
Neither their identity nor their exact location is being revealed for ethical reasons.
The journal, Nature, says the twins are identical on their mother’s side, but share only half their genes on their father’s side. This means they were a result of two sperm cells fertilising a single egg, which then divided to form two embryos - and each sperm (one male and another female) contributed genes to each child.
This is very unlikely and scientists believe the twins are probably unique.
Normally, twins either develop from the same egg which later splits to form identical twins — who share all their genetic material, or from two separate eggs which are fertilised by two separate sperm. This creates non-identical (fraternal) twins — who share on average 50% of their genetic material. Two sperm fertilising a single egg is only thought to happen in about 1% of human conceptions. Most embryos created this way do not survive.
But the twins are now toddlers, and doctors say they are progressing well.
Vivienne Souter, a geneticist at the Banner Good Samaritan Medical Centre in Phoenix, Arizona who investigated the case, said: “Their similarity is somewhere between identical and fraternal twins. It makes me wonder whether the current classification of twins is an oversimplification.â€
Charles Boklage, an expert on twinning at Eastern Carolina University in Greenville, North Carolina, said: “There is value in understanding that this can happen, but it is extremely unlikely that we will ever see another case.â€
The case is also reported in the journal, Human Genetics.
WONDERS never end! Scientists have revealed details of the world’s only known case of “semi-identical†twins.Born in the US, the twins, who were conceived normally, only came to the attention of scientists because one was born a hermaphrodite, with both ovarian and testicular tissue, while the other child is anatomically male.
Neither their identity nor their exact location is being revealed for ethical reasons.
The journal, Nature, says the twins are identical on their mother’s side, but share only half their genes on their father’s side. This means they were a result of two sperm cells fertilising a single egg, which then divided to form two embryos - and each sperm (one male and another female) contributed genes to each child.
This is very unlikely and scientists believe the twins are probably unique.
Normally, twins either develop from the same egg which later splits to form identical twins — who share all their genetic material, or from two separate eggs which are fertilised by two separate sperm. This creates non-identical (fraternal) twins — who share on average 50% of their genetic material. Two sperm fertilising a single egg is only thought to happen in about 1% of human conceptions. Most embryos created this way do not survive.
But the twins are now toddlers, and doctors say they are progressing well.
Vivienne Souter, a geneticist at the Banner Good Samaritan Medical Centre in Phoenix, Arizona who investigated the case, said: “Their similarity is somewhere between identical and fraternal twins. It makes me wonder whether the current classification of twins is an oversimplification.â€
Charles Boklage, an expert on twinning at Eastern Carolina University in Greenville, North Carolina, said: “There is value in understanding that this can happen, but it is extremely unlikely that we will ever see another case.â€
The case is also reported in the journal, Human Genetics.