Eli5: is it possible for a single grandparent to pass on their eye colour to their grandchild?

Question

Me and my partner both have brown eyes…
My side of the family have all brown eyes so I’m assuming we don’t have the blue eye gene.
My partners parents: his dads side have all brown eyes but his mother and aunts and grandfather have blue eyes. So my husband must be a carrier.
Will my brown eyed genes dominate his blue eye genes or is it possible for a blue eyed baby?
It’s so interesting how it works

In: Biology

Answer 1

Our DNA is split in chromosomes which are paired. Each chromosome of a pair carry a version of each gene, one from your father, one from your mother. A gene carry the information on how to build a protein, so when your cells create a protein, it reads one of the version of the gene and follow its instructions.

Now, some genes are expressive and some are recessive. the expressive will be the one that will affect the phenotype (appearing parts) of your body while the recessive will probably won’t affect the phenotype.

For the blood types for example, if we oversimplify, there are 2 genes that define your blood type: one for the letter, one for the + (or the -). The letter have 3 variations: A when it tells to make the protein A, B for the protein B and O for “no protein”. there are 2 types of +/- genes: the + which creates the + protein, and the – that don’t create any protein. Since your body will read each gene in your DNA, and that you have 2 different genes, it will read 2 genes for the letter and 2 genes for the symbol.

If one gene is A and the other is A, it’s easy, it will produce A because that’s the only instruction there are, same with B. If you have 1 A gene and 1 B gene, it will produce both (so your bloodtype will be AB). If you have A and O, then your body will read the A and create A, and will read the O and will create nothing, so your bloodtype is A. Same with B and O. The only way to be O is to have 2 genes that tells your body to not create any A or B protein.

Now, for the eye colour, blue eye is recessive (IIRC, it’s just that it tells to not create melanin in your eyes) and the brown eye is expressive (it tells to create melanin in your eyes). So if you only have “brown eye” gene, your baby will at least have 1 “brown eye” gene. And since that gene is expressive, it will most likely means that your baby won’t have blue eyes. But that depends a lot on the gene you carry (how much expressive it is) and on the blue eye gene your partner have.