What Eye Color Will My Baby Have? Math For Pregnancy Prediction

What color will your baby's eyes be? Image by Mike DeHaan

What color will your baby’s eyes be? (Click to expand) Image by Mike DeHaan

Although the main question expectant parents ask is, ‘Will my baby be healthy?’ it’s also fun to ask other questions – such as, ‘What eye color will my baby have?’

Baby Eye Color Predictor

How can we predict a baby’s eye color?

We expect that a Caucasian baby will have gray or blue eyes at birth, since the color pigments have not yet developed fully, and usually African and Asian babies have brown eyes from birth.

By nine months, most Caucasian babies settle into their adult color: blue, brown, green or hazel. Some children will change eye color all the way up to age three, so don’t get too comfortable with your baby’s eye color until he or she is in preschool, it could still change!

Regardless of the eye color your baby ends up with later on, but before he or she is born, there’s no way to know for sure. Can you The question, however, is to predict your child’s eye color before birth, based on the parent’s genetic legacy? Let’s start with the classic “blue versus brown” match-up, and deal with the simplest situation.

Genetics: Alleles and Genes and More

Mendel’s principles of genetics are fairly well-known for dominant versus recessive genes. Each gene consists of a pair of alleles. Each parent donates one allele, so the child inherits a pair of alleles. The chart in the image above is a essentially a Punnett square.

A person with two dominant brown alleles, ‘BB‘, will have brown eyes. Another, with two recessive blue alleles, ‘bb‘, will have blue eyes. The brown dominance means that a mixed gene, ‘Bb‘, will be expressed as brown-eyed. Two blue-eyed people will have a blue-eyed child. Since the parents must each have a ‘bb’ gene, they can only pass ‘b’ alleles to the next generation. However, brown-eyed parents have either a ‘Bb’ or a ‘BB’ gene. You only know that a brown-eyed person has a mixed ‘Bb’ allele if that person had one blue-eyed parent.

From the chart, we can see that a child with brown-eyed parents has one chance in eight, or 12.5%, of being blue-eyed; and then only if one parent has some possible blue-eyed ancestry. Again, a mix of blue-eyed and brown-eyed parents has a “2/8=1/4=25%” chance of a blue-eyed child.

However, there is no guarantee that the situation will be quite this simple. Hazel and green eye color can both result from a weaker “brown” contribution.

Blue Eyed, Brown Eyed, Hazel or Green?

When you’re pregnant, it’s natural to wonder what your new baby’s eyes will be like, not to mention whether you’re having a boy or a girl, or how tall will she be. Although there’s no way to know for sure, you can use math to calculate the chances of brown eyes vs. blue, and more.

© Copyright 2013 Mike DeHaan: Math, All rights Reserved. Written For: Decoded Pregnancy

Comments

  1. My husband has hazel eyes and I have dark brown eyes — thanks to my mom having bright green eyes and his mom having crystal blue eyes, we had one child with brown, one with hazel, one with green, and one with blue eyes!

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