Blue and blue cant make brown?

Question

Why is it that if both parents have blue eyes their child has to have blue even if there is another color somewhere in the family but if both parents have brown eyes then their kids can have different colored eyes?

Answer 1

a person will have 2 traits called alelles.  one of their traits is dominent and one is recessive.  the dominent trait is the trait u have and the recessive is one that u can pass off to ur children.  for each color, their alelles could be this: (the dominent or the trait u have comes first, then the recessive alelle)

Brown: BB, Bg, Bb (brown is dominent over all colors)

green: gg, gb (green is only dominent over blue)

blue: bb (blue is recessive to all colors)

when u have parents with blue eyes, their alelles have to be bb because green and brown is dominent over blue. (meaning if they had a brown or green alelle then their eyes would be green or brown not blue)

each parent will pass one alelle to their child so they can also have a dominent and recessive alelle. since they can only pass a blue, then there is a 100% chance their child will have blue eyes.

hope this helps!!!

Answer 2

Blue is a recessive gene.   To have blue eyes both parents must have passed on genes for eye color that are not dominant to blue.   After that the children of blue eye people will not have an eye color dominant to blue since they have no gene dominant to blue eye color in either parent to pass along.

Answer 3

That's just how it is. Get over it! ; )

Answer 4

well the only reason two people with brown eyes can have a kid with brown eyes is because brown is a dominant jean, Example: so that means if there was one parent with brown eyes and one with blue, chances are the baby will have brown eyes.  Now if the parents have two recessive jeans (like blue) then they defiantly will have a baby with blue eyes because there is no dominant jeans (brown eyes)getting in the way.

Answer 5

It is possible for someone in the family to have dominant brown eyes.  That person can be homozygous for brown (BB) or heterozygous for brown (Bb) - brown and blue gene but brown is dominant so it is the phenotype (visible trait).  Another sibling can have blue only if it is homozygous for the recessive blue (bb). You can show this and figure out other traits by using a punnett square.  I'll explain using eye color as it is the easiest and you can draw the punnett square as I explain so you can see for yourself how what you describe could happen:

Brown eyes (B) are dominant. Blue or green eyes (b) are recessive to brown, (although green are dominant to blue). What recessive means is that if there is ever a combination of a dominant gene with the recessive gene, the dominant is always exhibited. The easiest way to understand eye color and heredity is to draw a punnett square. I'll try to explain and you draw it on paper as I do so. Draw a square. Inside draw a cross so there are 4 sections. Now we add the genes. If either parent is homozygous (home = same) for brown eyes (B), every offspring will have brown eyes. However if both parents are heterozygous for eye color, that is, each has a dominant and a recessive gene (Bb) they will have brown eyes but carry the recessive gene. Now go to your square. Put dad on top. Above the top left square put a B and above the top right square put a b (This represents dad's Bb genetic make up for eye color). Now go to the left side. Next to the upper left box put a B and next to the lower left box put a b. (This is mom's Bb make up.) Now combine them. The upper left box would have a BB. The upper right box would have a B (from mom) and a b (from dad). The lower left box would have a b (from mom) and a B (from dad). The lower right box would have a bb (from each mom and dad). If you look at the results you will have 1 offspring that is homozygous for brown eyes (BB) and has brown eyes. You will have 2 offspring that are heterozygous for brown eyes (Bb) and have brown eyes, and 1 offspring that is homozygous for recessive blue or green eyes (bb).

The example above is one of complete dominance = whenever there is a B, brown will be exhibited. There is also incomplete dominance where neither gene is dominant. An example is flower color. If R represents red and Rp = pink and pp = white this is what happens. Make your box. Cross a red flower (R & R above the top 2 boxes) with a white flower (rr next to the two left boxes). When you cross them, all four boxes have Rr which means you have 4 pink flowers. Now let’s cross 2 pink flowers. Draw your box. Above the top left and right put R and r (genes for pink). Next to the left top and bottom put R and r. Now cross them like you did with eyes. You will end up with one RR red flower, 2 Rr pink flowers and one rr white flower.