A question about eye colour

[spaceviking]

My nephew (3 months) has blue-grey eyes, My brother has blue-grey eyes, his wife has brown eyes. His wife is Japanese(Born in Japan to Japanese parents) so it is extremely unlikely she would carry the recessive gene for blue eyes. How is this possible?

[Duckie]

My nephew (3 months) has blue-grey eyes, My brother has blue-grey eyes, his wife has brown eyes. His wife is Japanese(Born in Japan to Japanese parents) so it is extremely unlikely she would carry the recessive gene for blue eyes. How is this possible?

Eye colour is a polygenic trait, the BB bb model is just an approximation. Any eye colour can occur from almost all combinations of parents save those with extreme populations of dominant genes such as indigenous subsaharan africans.

Further, there are numerous ways an ancestor could have such a gene, even if we ignore that the simple blue=recessive model isn't correct. Maybe it was passed from tocharan to uyghur to han to japanese in some ancient diplomatic trysts over the ages. She could have some long inexpressed throwbacks to an Ainu ancestor. The nephew might have had a copy error in his DNA, or other genetic hijinx.

The true answer though is that eye colour genetics is more complex than a simple mendel chart.

[Count Chocula]

Even going by the Mendel chart, despite the genes for brown eyes being dominant, there's a 25% chance of the blue-gray recessive genes carrying through. Looks like your nephew beat the odds.

Personal anecdote: my mother has brown eyes. My father has green eyes. My sister has brown eyes. My two half-brothers, from my father's brown-eyed third wife, have brown eyes. I'm the firstborn, and my eyes are my father's green. Hey! A one-datum confirmation of Mendel's predictions! What are the odds of that? I have a blue-eyed cousin, inherited from his Irish mum. My cousin's brother has his dad's brown eyes. Even odds since aunt and uncle stopped at two kids.

My son has my wife's brown eyes. Maybe I should have more kids and go for the green....nah.

[Sir Sirius]

Babies are often born with light blue eyes, has something to do with melanin in the eyes. Your nephews eyes might still change their colour substantially. Though "baby blue" eyes usually disappear during the first 6 months or so.