Genetic Secrets of Eye Color: Decoding the Puzzle
Unravelling the Genetics of Eye Colour: A Deep Dive into Polygenic Inheritance
Human eye colour is a fascinating trait that has long intrigued scientists and the general public alike. The answer to the question of why our eyes come in so many shades lies in the complex world of genetics.
Polygenic Inheritance: The Key to Understanding Eye Colour
Eye colour is determined by polygenic inheritance, a concept that suggests multiple genes and their respective alleles work together to influence the amount and type of melanin pigment in the iris. This polygenic inheritance leads to a continuous range of eye colours rather than a simple dominant-recessive pattern [1][5].
The Role of Melanin in Eye Colour
The degree of melanin pigment in the iris, controlled by these genes, determines whether eyes appear brown (high melanin) or blue/green (lower melanin). Genes like TYR affect melanin synthesis, and mutations can cause conditions such as albinism with very low melanin in eyes [2].
Dominance, Alleles, and the Complexity of Eye Colour Inheritance
Brown eye colour alleles are generally dominant over blue, but because many genes are involved, eye colour inheritance is more complex than Mendel’s simple single-gene dominant-recessive model. Alleles interact additively, and multiple possible alleles exist at various loci [3][5].
The Main Players in Eye Colour Genetics
The gene responsible for eye colour inheritance is called OCA2. Alleles are like different versions of genes, with some alleles being dominant and others recessive. SLC24A4 controls how melanin is distributed in your eyes, causing variations in the shade of brown eyes. HERC2 affects the amount of melanin, a pigment that gives your eyes colour [4]. Variations in the SLC24A5 gene can produce green eyes, a mesmerizing shade found in parts of Central and Eastern Europe [6].
Environmental Factors and Epigenetics
While genetic makeup largely determines eye colour, epigenetic mechanisms and environmental factors may affect gene expression, though their role in eye colour is less direct compared to other traits [4]. For instance, lower temperatures in the womb favor lighter eye hues, while warmer environments can result in darker irises [7].
The Genotype-Phenotype Connection
Each gene has two different versions called alleles. Genotype is the genetic makeup that underlies your phenotype, which is the outward expression of your genes, like your eye colour, height, or love of cheesy jokes. Each pair of genes is located on a chromosome [8].
A Surprising Twist: Brown-Eyed Parents and Blue-Eyed Children
It's possible for two brown-eyed parents to have a blue-eyed child, although it's not very common. This quirk of genetics highlights the complexity of eye colour inheritance [9].
As we age, the melanin pigment that gives our eyes their colour may diminish, leading to a lightening of the iris [7]. Understanding the concepts of alleles, dominant and recessive traits, and genotypes is crucial for comprehending the inheritance patterns of eye colour.
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5941137/ [2] https://ghr.nlm.nih.gov/gene/TYR [3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5941137/ [4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5941137/ [5] https://www.nature.com/articles/s41586-018-0508-6 [6] https://www.nature.com/articles/s41586-018-0508-6 [7] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5941137/ [8] https://ghr.nlm.nih.gov/gene/OCA2 [9] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5941137/
- Eye colour, influenced by polygenic inheritance, is determined by multiple genes working together to affect the amount and type of melanin pigment in the iris [1][5].
- Alleles, like different versions of genes, play a significant role in eye colour. The gene responsible for eye colour inheritance is called OCA2, with SLC24A4 and HERC2 being other major contributors to variations in eye colours [4].
