Wednesday, January 10, 2007

Mirror Image Twins

Discussion of cow twins led Lauren to remember seeing a TV show in which "mirror image twins", human twins, were shown. Are there really mirror image twins, she asked? I've Googled it, and yes, there are, which fits in nicely with our Biology discussions of late:

What are mirror image twins?
Mirror image twins are identical twins that result when a fertilized egg splits later in the embryonic stage than usual, typically from day 9 to 12. Mirror image twins tend to exhibit characteristics with reversed asymmetry (e.g., one twin is left-handed and the other is right-handed). If this split happens much later than this, then the twins can be co-joined. A DNA-based zygosity test cannot determine is twins are mirror image twins.

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