What color eyes will baby have if mother has brown eyes and father has blue eyes?

Brown eye gene = B

Blue eye gene = b

Each person has two copies of the eye color gene in their genome, one inherited from each parent. Now if both parents only carry the gene for brown eyes, BB and BB, then their child will receive one B from each parent, ending up as BB. The same works for blue eyes, if that's the only gene both parents carry, bb and bb. Each parents gives on b to the child, who ends up as bb.

If you have one parent who only has the gene for brown eyes, BB, and one parent who only has the gene for blue eyes, bb, then all the children will have brown eyes. Example: One parent gives a B, the other gives a b. Bb = brown eyes. Here's why: When you have two alleles (coding sequences) from genes that are at odds with each other, one version will override the the other. When dealing with eye color, B always dominates b. But these children now carry the b gene in them, and could pass it down to their own children. Some of them, depending on the other parent, could end up with blue eyes.

If one parent is Bb, and the other is bb, then each time they have a child, there is a 50% chance it will have blue eyes. Example: First parent is Bb, second parent is bb, then their children will end up as either Bb, bb, Bb, bb. If both parents carry the genes for brown eyes and blue eyes, then each time they have a child, there is a 25% chance it will have blue eyes. Example: First parent is Bb, second parent is Bb, then their children will end up as either BB, Bb, Bb, bb.