A woman with dark-brown eyes has identical-twin green-eyed daughters. Their dad also has brown eyes, as did everyone else in the previous three generations, with two exceptions: a maternal great grandmother and a paternal grandmother, both with blue eyes.
Given the absence of green eyes in the recent family history, how could this have happened?
A cool Web site, Ask the Geneticist, gives a very clear explanation of why the green genes may go for generations without a trace. Stanford neuroscience graduate student Zhaoqing (Ching) Ding lays out the various combination of dominant and recessive genes that determine eye color. The site is hosted by the Tech Museum of Innovation in San Jose and has been responding to questions from the public since 2005.
Photo by Beautiflaw