slb@drutx.UUCP (Sue Brezden) (08/20/85)
andrew@grkermi.UUCP (Andrew W. Rogers) writes: > >My wife is left-handed, but >her identical twin is right-handed... figure that one out! > Actually, I have heard that this is not uncommon among identical twins. One twin will be a mirror image of the other. I remember a book that showed pictures of twin's heads, with the hair growing in whorls in opposite directions. Does anyone know why this happens? Are fingerprints reversed? Come to think of it, are fingerprints the same on identical twins? Why does this happen only sometimes? -- Sue Brezden Real World: Room 1B17 Net World: ihnp4!drutx!slb AT&T Information Systems 11900 North Pecos Westminster, Co. 80234 (303)538-3829 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Your god may be dead, but mine aren't. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
hes@ecsvax.UUCP (Henry Schaffer) (08/21/85)
> Come to think of it, are fingerprints the same on identical twins? > Sue Brezden > From Levitan and Montague, "Textbook of Human Genetics" (2/e). "The digital, palmar and plantar ridge counts and dermal patterns on homolateral limbs tend to be strikingly alike in twins. ... Monozygous [one egg - identical] twins may, however, differ very appreciably in their dermatoglyphic traits owing, presumably, to factors operative upon them during development." The discussion does mention that sometimes identical twins do have identical dermal patterns, and that identical dermal patterns does show that the twins are identical. --henry schaffer
charli@cylixd.UUCP (Charli Phillips) (08/21/85)
In article <233@drutx.UUCP> slb@drutx.UUCP (Sue Brezden) writes: >andrew@grkermi.UUCP (Andrew W. Rogers) writes: >> >>My wife is left-handed, but >>her identical twin is right-handed... figure that one out! >> > >Actually, I have heard that this is not uncommon among identical >twins. One twin will be a mirror image of the other. I remember >a book that showed pictures of twin's heads, with the hair growing >in whorls in opposite directions. > >Does anyone know why this happens? Are fingerprints reversed? >Come to think of it, are fingerprints the same on identical twins? >Why does this happen only sometimes? > My understanding (based on the human medical genetics class I took in college a few years back) is that handedness is determined, not by chromosomal genes, but by genetic material in the cytoplasm of the ovum. (This was called "the maternal effect" or something similar by our professor.) Since there is no mechanism to make sure everything in the cytoplasm of one cell is split evenly between the two daughter cells (or rather, since no such mechanism was known at the time I took the course), it is possible for the fertilized egg to split "unevenly". In the case of twins, when the fertilized egg separated into two cells, and the two cells separated into two separate zygotes, the genetic material in the cytoplasm may have been different, resulting in differences in handedness, hair whorls, and so on. (Of course, I freely admit this information is based on recollection, and may be incorrect or out of date.) charli
dgary@ecsvax.UUCP (D Gary Grady) (08/22/85)
A recent article in SCIENCE (18 Aug 85) indicates left-handed and
ambidextrous persons have a larger corpus callosum than right-handers.
The corpus callosum is the structure that connects the hemispheres. One
possibility is that in left-handers and the ambidextrous, brain function
is not as specialized between the two hemispheres of the brain, so more
interhemispheric communication is needed. This would suggest that in
twins with different handedness, their brains would be quite
significantly different.
Nature-vs-nurture studies involving twins have tended to assume
identical twins have the same "nature" (so any observed difference
would presumably be due to environmental factors). If it is true that
identical twins tend to have different handedness, this assumption may
be invalid.
--
D Gary Grady
Duke U Comp Center, Durham, NC 27706
(919) 684-3695
USENET: {seismo,decvax,ihnp4,akgua,etc.}!mcnc!ecsvax!dgary