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Two Colored Eyes
Name: Jo P.
Status: educator
Age: 50s
Location: N/A
Country: N/A
Date: 1999-2001
Question:
What is it called when a person has two different colored
eyes? (one blue and one hazel)
Replies:
This condition is usually the result of what is termed a genetic mosaic. A
mosaic is something which occurs in females for traits which are controlled
by genes on the X chromosome. In organisms with the double XX genotype
female, one of the X chromosomes gets turned off early in embryonic
development, apparently at random. So half of the cells have an active
paternal X and half have an active maternal X. Although there are genes on
other chromosomes which are related to eye color, there may also be a gene on
the X chromosome which has an effect.
Because the process of turning off one of the X chromosomes occurs when the
embryo is still very small, and because during the further development all of
the cells derived from one cell usually stay close together, we should expect
that it is usually true that all of the cells in the irises, which give color
to the eyes, have the same active X chromosome. However, it may sometimes
happen that some of the cells in one of the irises have the other X
activated. This can cause these cells to be a different color from the
others.
The condition of genetic mosaic can happen in males, however, the mechanism
is not clearly understood and the occurrence is even more infrequent than the
occasional mosaic female.
Paraphrased and submitted by Cherie Breffeilh
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Update: June 2012
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