Monday, April 09, 2007

Semi-identical twins

You've heard of fraternal and identical twins. But apparently, there is a (rarely-occurring) third type that scientists have dubbed "semi-identical twins." A recent article in the journal Nature details the only-known set of such twins, who developed when a single ovum was fertilized by two sperm. This situation does occur in an estimated 1% of all pregnancies, but usually the child does not survive.

The semi-identical twins were discovered because one of them is physiologically hermaphrodite, displaying features of both sexes. (The other appears as a normal male; however, both have a mixture of genetically male and female cells.)

See here for more.

3 comments:

Nancy C. Brown said...

This caught my eye, as my sister conceived a child, and he died in utero at 16 weeks, due to two sperm penetrating one ova, but it didn't split, and was incompatible with life. I didn't realize how common this was. (1% seems high to me) We probably would never have known what went wrong, but it turned into a molar pregnancy and she was dangerously ill.

Alice said...

Fascinating.

My husband is an identical twin, and I am always amazed by twin facts.

Ana Braga-Henebry said...

Our goddaughter is an identical twin, and I have been fascinated by twins since attending a lecture by the late (and wonderful) Lejeune. This is fascinating--and my bet is-- there is more to twins than it is known...