Parents with brown and blue eyes: what colour will the baby's eyes be?
Brown eyes are the most likely, at 50%. The full odds: brown 50%, green 25% and blue 25%.
Most likely eye colour
Brown
Many babies are born with lighter eyes that darken during the first year. The colour has usually settled by the first birthday and can still shift a little until about age 3.
Estimate from a two-gene model that assumes each parent carries hidden versions of both genes.
A simplified estimate for fun. Real genetics is more complex.
How we work it out
The model uses two genes. bey2 has a brown version (B) and a blue one (b); gey has a green version (G) and a blue one (b). Each parent passes on one version of each gene, so each parent has four equally likely combinations and the square has 16 boxes. Any B gives brown eyes; otherwise any G gives green; otherwise the eyes are blue.
A brown-eyed parent is assumed to carry a hidden blue version of both genes: bey2 Bb, gey Gb.
A blue-eyed parent has only blue versions of both genes: bey2 bb, gey bb.
| b b | b b | b b | b b | |
|---|---|---|---|---|
| B G | brown | brown | brown | brown |
| B b | brown | brown | brown | brown |
| b G | green | green | green | green |
| b b | blue | blue | blue | blue |
- Brown: 8 of 16 boxes
- Green: 4 of 16 boxes
- Blue: 4 of 16 boxes
Frequently asked questions
Can parents with brown and blue eyes have a baby with brown eyes?
Yes. In the two-gene model it happens 50% of the time.
Can parents with brown and blue eyes have a baby with green eyes?
Yes. In the two-gene model it happens 25% of the time.
Can parents with brown and blue eyes have a baby with blue eyes?
Yes. In the two-gene model it happens 25% of the time.
- MedlinePlus Genetics (US National Library of Medicine): Is eye color determined by genetics?
- The Tech Interactive, Ask a Geneticist: What are the chances my child will have red hair and blue eyes?
- Eiberg H, Mohr J. Major genes of eye color and hair color linked to LU and SE. Clinical Genetics 1987;31(3):186-191
- American Academy of Ophthalmology: 20 Things to Know About Children's Eyes and Vision
- Jabbehdari S et al. Colour change in the newborn iris: 2-year follow-up of the Newborn Eye Screening Test study. Acta Ophthalmologica 2019