If you have more questions about eye color, check out these informative website: http://www.allaboutvision.com/conditions/eye-color.htm
Article on how Blue Eyed Parents can have Brown Eyed children
Calculate the Probability Your Child Will Have a Certain Eye Color
Wikipedia has a wealth of information on eye color, including anomalous (unusual) conditions in regards to eye color.
Also below, I go into depth about how genes control eye color:
Eye color is commonly taught as a trait controlled by one gene. However, eye color is a polygenic trait meaning it is controlled by multiple genes. These genes in combination may allow large amounts of melanin (a brown pigment) to be deposited or less melanin to be deposited. For example, a person who has genes that deposit larger quantities of melanin would have either black skin, black hair, and/or dark brown eyes. A person who has the genes that deposits smaller quantities of melanin would have white skin, blonde hair, and/or blue eyes.
I don't talk about the genotypes associated with eye color in this video-- which would be quite complicated. Genotypes are the underlying genes associated with a trait. For example, cleft chin (or butt chin) genotype is cc, and not having cleft chin is CC or Cc. Why two letters? Because you receive one letter (or one allele) from each parent, one coming from dad's sperm cell and one coming from mom's egg cell. Depending on the trait, one allele might dominate over the other allele. For example, a person with even one "C" will have no cleft chin, but someone has to have 2 "c's" in order to have cleft chin. Having no cleft chin is the dominant trait (since it masks over the cleft chin allele) and having a cleft chin would be considered the recessive trait (since you need both alleles to express this trait).
Now eye color is slightly complicated because there are said to be two genes associated. with eye color (thus, eye color being a polygenic trait). For example, BBGG genotype would be someone has only the genes for dark brown eyes, depositing the greatest amount of melanin, whereas bbgg would be blue eyes, depositing the least amount of melanin.
But what about green eyes?
The green eye genotype would have to be bbGg or bbGG. If a person had even one big "B" that person would have brown eyes.
So brown eyes can be any of the following genotypes: BBGG, BBGg, BBgg, BbGG, BbGg, Bbgg. But those genotypes might have varying shades of brown-- think of each big letter depositing the greatest amount of melanin and every small letter depositing less melanin.
What if two parents, one with dark eyes and one with light colored eyes had children? There's a whole host of possibilities that can rise from such a cross because it'd be difficult to determine the exact genotype of both parents, thus, it'd be difficult to determine the exact genotypes of the children.
For example, lets say the dark eyed parent had a genotype of BbGG (one possible genotype of brown eyes), and the light eyed parent had a genotype of bbGg (one possibe genotype of green eyes). After conducting a dihybrid punnet square cross, you would find that the parents would have 25% likelihood of having kids with BbGG genotype (brown eyes), a 25% likelihood of having BbGg genotype (possibly lighter colored eyes), 25% likelihood of having bbGG (green eyes), 25% likelihood of having (bbGg possibly lighter green eyes).
It's a complicated cross, but it shows how siblings can have varying shades of eye color depending on the genotypes of their parents. What you can be sure of is that at least some of the offspring will be carriers for light colored eyes ('b" or "g") and thus, have the possibility of having children with light colored eyes if the other parent carries similar genes.
In this video, I explain how melanin plays a role in eye color. In addition, one can see a noticeable difference between two brown-eyed individuals, where the brown-eyed individual with a green-eyed and brown-eyed parent has noticeably different colored eyes compared to an individual with two brown-eyed parents.
By the way, the person with the green-eyed and brown-eyed parent is my boyfriend, Jon.
The person with the two brown-eyed filipino parents is me!
And the dogs are my dogs, Chippy and Butters.
Artist: Kevin MacLeod
Title: Snow Queen