CAN TWO BLUE EYED PARENTS
HAVE A BROWN EYED CHILD?
With our middle school biology knowledge, we know
that two brown eyed parents may have a child with
blue eye. This is a basic concept but there are those
cases in which parents with blue eyes may have a child
with brown eyes. How is that even possible?
What we learned was the Mendelian Genetics. Here,
the control of eye color is simplified down to a very
basic level where it is considered to be controlled by
only two genes. Allele – a form of a gene- coding for
darker eye color is dominant and for lighter colors it
is recessive. It is accepted that a green or blue eyed
person has two recessive alleles as this is the only way
for a recessive character –green or blue eye color in
this case- to be seen on the phenotype – the physical
appearance of the individual (Allott & Midroff , 2014).
As two blue eyed parents both only have recessive
genes, according to Mendelian Laws they will pass
on only recessive alleles to their offspring so the eye
color of the new generation is also supposed to be
blue, too. Accordingly, having a brown eyed child is
impossible for blue eyed parents. The phenomenon
was explained later on when scientist have discovered
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THE CLAPPER 2016 - 2017
that inheritance of eye color is more complex than
this.
In order to understand the gene inheritance of the
eye color it is a good idea to first look at the eye
color expressions. Eye color is caused by the pigment
melanin produced in your eye. The more melanin
that you produce, the darker eye color you have. So,
people with brown eye synthesize lots of melanin
whereas the people with blue eye synthesize none
(MacDonald, 2014). Gene responsible of melanin
production in human eye is OCA2. When OCA2 gene
is expressed the pigment production is initiated and
the eye color darkens. But OCA2 cannot be expressed
all by itself. There is another gene HERC2 which causes
the expression of OCA2 gene. In some cases, genes
mutate which means that genetical information of the
chromosomes are being changed which may disqualify
the gene from doing its function. For a person who has
a mutated OCA2 gene it is impossible to synthesize
the melanin. The same applies for a person who has
a normal OCA2 gene but mutated HERC2 gene as they
cannot express OCA2 gene at all. So for both of these