How can two brown-eyed parents have a blue-eyed baby?

Most of our characteristics, such as eye colour, are encoded by a pair of alleles. These are different forms of the same gene, one inherited from the father and one from the mother. You can get dominant and repressive alleles. Dominant alleles, such as brown-eye alleles, only need one copy of the allele in order for the characteristic to be expressed. Repressive alleles, such as blue-eye alleles, need two copies of the allele to be expressed. If a mother and father both have brown eyes but each carry the repressive blue-eye allele (i.e. they are heterozygous), there is a chance that the offspring may inherit two blue-eye alleles: one each from the mother and father. Thus the child would have blue eyes. We can use punnett squares to work out the probability of the offspring inheriting different allele combinations. 

Amber S. A Level Biology tutor, GCSE Biology tutor, GCSE Chemistry tu...

6 months ago

Answered by Amber, a GCSE Biology tutor with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


£18 /hr

Lewis M.

Degree: Biology (Masters) - Bristol University

Subjects offered: Biology, Maths


“About Me: I am a Biology student at Bristol University. I have always loved science and maths and I hope this will come across in my sessions! I have been invloved with tutoring for the majority of my school life, taking time out of ...”

£18 /hr

Elizabeth J.

Degree: Veterinary Science (Bachelors) - Bristol University

Subjects offered: Biology, Spanish


“Hi I'm Liz and I'm a first year vet student at the University of Bristol! I'm really excited to tutor you and people have always said I'd be a good teacher! Anything you are stuck on please do say and I'll do my best to explain it in a...”

MyTutor guarantee

£18 /hr

Lucy W.

Degree: Bsc Biological Sciences (Bachelors) - Exeter University

Subjects offered: Biology, Spanish+ 1 more


“I am currently studying Biological Science at Exeter University - a course that I absolutely love.  I like to think I am a patient and considerate person, having experience tutoring younger family members, and other students whilst I ...”

About the author

Amber S.

Currently unavailable: for regular students

Degree: Molecular and Cellular Biochemistry (Masters) - Oxford, Magdalen College University

Subjects offered: Biology, Science+ 2 more


“Hello! I am a student reading Biochemistry at the University of Oxford. I greatly enjoyed science and math when I was at school and would love to help other students experience it in the same way that I did. The Sessions All stud...”

MyTutor guarantee

You may also like...

Other GCSE Biology questions

What does the nervous system consist of and what does it do?

What is osmosis?

(Biology GCSE) How does the body control blood glucose concentration?

How do vaccines cause immunisation to disease?

View GCSE Biology tutors


We use cookies to improve our service. By continuing to use this website, we'll assume that you're OK with this. Dismiss