If you are one of the many expectant parents asking yourself “what color eyes will my baby have?” genetics can give you an answer. Or at least a hint of which colors are more likely based on yours and your partner’s eye color and family history. While there is not a perfect genetic baby eye color predictor, an eye color calculator can only offer a list of what are the most likely colors for your baby’s eyes. It’s all in the genes!

Genes and Alleles

Gregor Mendel, the father of modern genetics, discovered that not all genes are the same. Each living being has different variations of the same gene (or genetic locus), and each of those variations are called alleles. Each organism has two alleles of the same gene, one coming from each progenitor: if they are the same the organism will be homozygous, otherwise it will be heterozygous with respect to that particular gene.

Alleles can be dominant or recessive. A dominant allele manifests itself if it’s present, however a recessive one won’t express itself unless there is not a dominant allele present. In human reproduction, a baby will get two alleles for each gene, one from mum and one from dad. However, not both of them will manifest. Some genetic diseases such as Cystic Fibrosis are considered recessive because two copies of the allele causing the disease need to happen in order for the disease to manifest.

But what does this have to do with predicting baby’s eye color?

How Do Eye Colors Work At Genetic Level

Eye color is believed to be controlled by just a few genes, so depending on which version the baby inherits from their parents he will have one eye color or another. There are several things that can affect eye color and tone. For example, not all blue eyes are the same, green eyes can vary from emerald to hazel and brown eyes come in all degrees of darkness and warm. So this baby eye color calculator will restrict itself to giving you an idea of whether Baby’s eyes will be mostly brown, green or blue.

Green eyes are recessive

Green eyes are recessive

There are currently 3 genes that have been identified as affecting human eye color, and two of them, called Bey2 (chromosome 15) and Gey (chromosome 19) can be used to predict baby eye color based on the parents phenotype.

Genetic Basis of a Baby Eye colour Calculator

Bey2 has two forms, one recessive and one dominant:

  • B causes Brown eyes and is dominant over b and both Gey alleles
  • b causes Blue eyes and is recessive

Gey has two alleles:

  • G causes Green eyes and is dominant over Bey2’s b and g alleles
  • g causes Blue eyes

Your baby’s eye color will depend on which combination of those eyes he inherits from you and your partner. If Baby has a single copy of the B allele, she will have brown eyes. If Baby has a copy of the G allele and no copy of the B allele, she will have brown eyes. If Baby only has b and g alleles you will have blue eyed baby.

There are 9 possible combinations of the above Alleles.

The following combinations are for Brown eyes:

BBGG, BbGG, BBGg, Bbgg

The following combinations are for Green eyes:

bbGg, bbGG

And the following allele combinations would give your baby blue eyes


Baby Eye Color Predictor Based On Alleles And Probability

If both parents have Blue eyes, then they will give the baby a b and a g allele each. The baby will have blue eyes (however, since there are more genes involved this is not true 100% of the time. But the likelihood of it happening is very high).

If both parents have Green eyes that means they don’t have any dominant B allele, and as such they can’t have brown eyed children. Their children will most likely have green or blue eyes. Given that the parents have green eyes, we know that they have at least one G allele each that could be passed to their progeny. They will also have both a b allele, and no dominant B allele. Their babies could be:

bbGG (if both parents are G homozygous, or the baby inherits the G allele from one of them)
bbGg (if at least one of the parents has a Gg pair
bbgg if both parents are heterozygous for the Gey gene, and the baby inherits both g recessive versions. This would result on a blue eyed baby with parents who have green eyes.

If there are people with blue eyes on yours and your partner’s family, the baby has a 25% possibility of having blue eyes too. If there are blue eyes on only one side of the family (or no blue eyes at all), the baby is more likely to have green eyes.

If both parents have brown eyes, their babies can have any eye color and things get a bit more complicated. We will need to look at the grandparents to try and identify whether the parents have any recessive allele that could be passed to their children. For example, even if both parents have brown eyes, if at least one of the grandparents has blue or green eyes the baby could be born with eyes of that color. This is why sometimes babies resemble their grandparents a lot! However, the possibilities are much smaller.

Since both parents have brown eyes, we can assume that each of them will have at least one B allele. If neither parent has anything but brown eyes on the family, they could both be BB and the baby will be BB as well, which means the baby eye color predictor would predict brown eyes. If there are blue or green eyes on both sides of the parental families, then things get more interesting.

Let’s look at the parents’ families. If any of the grandparents have blue eyes, the parent is most likely Bbgg, as she would have inherited a recessive bg pair from her blue eyed grandparent. If any of the grandparents have green eyes, they are most likely BbGg or BbGG, as the dominant G allele would have been inherited from the green eyed grandparent, along with a recessive b gene. You can use Punnet squares to calculate the probability of each possible baby’s eye colors by filling all the possible combinations between the genes provided by each parent.

Occasionally a family where everybody has brown eyes has some members with green or blue eyes, this is because the recessive allele is transmitted but never expressed until two recessive genes are together.

It is very common to wonder what color your baby’s eyes will be like while you are expecting. While a genetic baby eye color predictor can give you some clues as to what eye color will your baby have, the truth is that the only way of knowing if Baby has inherited Granma’s emerald eyes is by waiting a few months after birth, when the baby’s eye color will become fixed.

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