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...

9 months ago

Answered by Amber, a GCSE Biology tutor with MyTutor

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


£24 /hr

Sioned D.

Degree: Law (Bachelors) - University College London University

Subjects offered:Biology, Maths+ 4 more

-Personal Statements-

“Hello! I'm a University College London Final year Law Student with a great deal of tutoring experience in English, Maths, Sciences and Entrance Exams. ”

£30 /hr

Jessica-Lily H.

Degree: MRes Experimental Neuroscience (Masters) - Imperial College London University

Subjects offered:Biology, Psychology


“Top tutor from a world leading university- ready to do all I can to help you get your head around that tricky subject!”

£18 /hr

Rachael D.

Degree: MRes Ecology and Environment (Masters) - Sheffield University

Subjects offered:Biology, Science+ 1 more


“Postgraduate student in Ecology and Environment here to help with all things biology, ecology and conservation. ”

MyTutor guarantee

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

Define 'biomass'

Describe how living things are involved in the constant cycling of carbon.

How do I remember what adaptations plants and animals have in dry conditions? How would I answer this in a question?

What is anaerobic and aerobic respiration?

View GCSE Biology tutors

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