Can two brown-eyed parents have a blue-eyed child?
Eye color, like the many physical traits that we possess stem from our internal genetic infrastructure (genotype) inherited from both our parents. Humans traditionally have 46 chromosomes, all of which contain genes that express our physical outlook (phenotype).
Before reading more about How two brown-eyed parents have a blue-eyed child? I suggest you go through below post to understand more about eye color genetics.
How is eye color genetically inherited?
The interactions between various genes have been found to determine color pigmentation in humans. However, specifically, HERC2 and OCA2 genes located on chromosome 15 are associated with eye color. Different studies have shown that specific Single Nucleotide Polymorphism (SNP) position on the OCA2 gene determines the presence of brown or blue eyes.
The research was done to find out the genes that are associated with human pigmentation showed that HERC2 SNP rs12913832 was statistically significant when tested for the association with eye color. Within this SNP two alternative forms of a gene (allele) C and T DNA bases determines the color of the eye.
Since all chromosomes come in pairs, possible variations of this gene would be CC, TT (homozygous), and CT (heterozygous) with one allele being inherited from each parent.
Statistical results from a research done by Branicki et. al. (2009) showed the CC gene expressed 88.9% of blue-eyed subjects, CT and TT gene both expressing brown/black-eyed subjects with 84.4% and 15.6% respectively.
Is there a possibility that two brown-eyed parents of having a blue-eyed child?
As research has shown that genes are associated with eye color, we can now predict if it is possible that two brown-eyed parents to have a blue-eyed child. This can be easily determined by using a Punnett’s square, where possibilities of the parent genotypes are used to check the probability of what genotype a child would inherit.
Since both parents are brown-eyed their genotypes would either be CT and CT, TT and TT, or CT and TT
Conclusion: If both brown-eyed parents are both heterozygous CT there would be a 25% chance that their child would inherit the CC gene and have blue eyes.
Conclusion: If both brown-eyed parents are both TT none of their children would have blue-eyes.
Conclusion: If both brown-eyed parents are either CT or TT none of their children would have blue-eyes.
From the research by Branicki et. al. (2009), we have done a Punnett’s square test and shown that both parents have to be heterozygous CT in order for their child to have 25% probability of inheriting blue eyes.
This was also discussed in an article by www.science daily.com where they highlighted that it is possible for brown-eyed parents to have a blue-eyed child.
So don’t go running out to do paternity tests just yet when you see your child with a different eye color. He/she might just have been the 25% of the gene pool having blue-eyes even though you and your spouse have brown-eyes.
References for more info :
Branicki, W., Brudnik, U. and Wojas-Pelc, A. (2009), Interactions Between HERC2, OCA2 and MC1R May Influence Human Pigmentation Phenotype. Annals of Human Genetics, 73: 160–170. doi:10.1111/j.1469-1809.2009.00504.x
Springer. “Blue Eyes — A Clue To Paternity.” ScienceDaily. ScienceDaily, 23 October 2006. <www.sciencedaily.com/releases/2006/10/061023193617.htm>.
Sturm, R. A. and Larsson, M. (2009), Genetics of human iris colour and patterns. Pigment Cell & Melanoma Research, 22: 544–562. doi:10.1111/j.1755-148X.2009.00606.x