Need a refresh w genetics&offspring eyecolor-are brown eyes always BB?Can brown be Bb like green/hazel?

Question

Obviously, two blue-eyed parents (both bb) cannot have a brown-eyed child--but what about a blue-eyed parent (bb) and a brown-eyed parent (BB)? Since brown is always dominant, can the offspring have Bb, and be brown-eyed - if Bb assumes the dominant B, instead of autosomal recessive,(where green or hazel eye color would result) On Bb, doesn't eye color of brown or green/hazel depend on which gene is activated--the big B or little b? How can you break it down further to determine how many Brown-eyed and how many green/hazel/other children would result from a (BB) parent (both of BB's parents had brown eyes) and blue-eyed parent (bb)? No bullshit examples or personal opinions, please.

Answer 1

Steve is right, eye color is controlled by more than one gene.  We do know quite a lot about the two major genes involved:  B & G, and there epistatic interaction (that just means how two genes work together to make one trait).

If you are dominant at the B gene (so BB or Bb), then you have brown eyes, period, and it doesn't matter what you have for the G gene.  But, if you are homozygous recessive at the B gene (bb), then it does matter what kind of alleles you have for G.  If you're bb and dominant at G (so Gg or GG), then you have green eyes.  If you're homozygous recessive for both genes bbgg, then you have blue.

The various shades, like hazel, gray, etc. are controlled by other minorly contributing genes and environment.

Answer 2

Have you done a Punnett square for it?  Or maybe that's what you need a refresh on?  xD  That's the easiest way I can see to do it.

For BB x bb, all the offspring would be heterogenous (Bb).  And you're right, eye color would depend on which of the genes is activated.  Looks like those kids are going to be all mixed up.  xD

Answer 3

B is always dominant and b is always recessive. A kid with BB or Bb genotype will have brown eyes. A kid with bb genotype, will have blue eyes.

A blue eyed parent (bb) and a homozygous brown eyed parent (BB) will only have heterozygous brown eyed (Bb) kids. If the brown eyed parent is heterozygous (Bb) then 1/2 of their kids will be heterozygous brown eyed (Bb) and the other half will be blue eyed (bb) and therefore homozygous.

Answer 4

Well, it's none of those, actually.

See, eye color is determined by more than one gene, and by the amounts of pigment called 'melanin' in each gene. If all the genes have a lot of melanin, then you get darker colored eyes, like brown. If all the genes have very little melanin, then you get lighter colored eyes, like blue. But, because there are multiple genes, there are all sorts of variations of how much melanin there is, which is why you get so many different shades of blue, brown, green, and hazel.

So, no, it doesn't depend on which gene is activated when there is a mix (like Bb). It has more to do with the amounts of melanin in each gene to put towards the coloration of the eye. The 'B' gene will have a lot of melanin, while 'b' will have very little melanin, so it could be anywhere from green, to hazel, to light brown. It is also possible to be a very dark blue color.

You can't really break it down to figure out what colored eyes the offspring of certain parents are, because, like I said, it's more than just two genes that determine eye color. Realistially, the blue eyed parent probably has some genes with more melanin in them, but they happen to have more genes that have less melanin, which makes their eyes blue. So, plenty of their kids could have brown eyes, or blue eyes (because the brown eyed parent probably has some genes with less melanin) and every color variation in between.