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THE BABY BEAT – February 4, 2015
D. Gary Benfield, M.D.
Can blue-eyed parents have a child with brown eyes?
I was recently asked by a lawyer if two blue-eyed parents had a child with
brown eyes, did that suggest the child’s biological father was someone else?
I replied yes, and furthermore that “someone else” had brown eyes. Here’s how
I explained it.
The genes for traits such as eye color occur in pairs on our chromosomes. Let’s
say B is the gene for brown eyes and b is the gene for blue eyes. If a person’s
gene-pair for eye color is BB, she will have brown eyes. If her gene-pair for eye
color is bb, she will have blue eyes. But if her gene-pair for eye color is Bb, she
will still have brown eyes because B dominates b. Put another way, b is recessive
to B.
So, if a blue-eyed male’s sperm carrying the bb gene-pair for eye color fertilizes
a blue-eyed female’s egg carrying the bb gene-pair for eye color, four
combinations are possible: bb, bb, bb, bb. Thus, all of their children will have blue
eyes, right?
So, if their child has brown eyes, the child’s biologic father is someone else, and
mom has some explaining to do. Moreover, the biologic father has to have either a
Bb or BB gene-pair for eye color, meaning he has to have brown eyes, in order for
his child to have brown eyes, too, right?
THE BABY BEAT – February 4, 2015
Can blue-eyed parents have a child with brown eyes?
Now, let’s consider the opposite question: Can two brown-eyed parents have a
child with blue eyes? The answer is yes, and here’s why.
Based on what we’ve already learned, if a brown-eyed male’s sperm carrying
the BB gene-pair for eye color fertilizes a brown-eyed female’s egg carrying the
BB gene-pair for eye color, four combinations are possible: BB, BB, BB, BB.
Thus, all of their children will have brown eyes, right?
On the other hand, if one brown-eyed parent’s gene-pair for eye color is Bb and
the other brown-eyed parent’s gene-pair for eye color is BB, the four possible
combinations are BB, Bb, BB, and Bb. Again, all of their children will have
brown eyes because B dominates b, right?
But, if both brown-eyed parents carry the gene-pair Bb, the four possible
combinations are BB, Bb, Bb and bb. In this case, each of their children will have
a 1-in- 4 chance of inheriting the gene-pair bb, which causes blue eyes.
So, yes, two brown-eyed parents can have a child with blue eyes.
* * * *
On an unrelated topic, a study published in the January issue of Pediatrics, the
official journal of the American Academy of Pediatrics (AAP), sought to
determine how frequently potentially hazardous bedding is used during sleep for
infants under one year of age.
THE BABY BEAT – February 4, 2015
Can blue-eyed parents have a child with brown eyes?
Currently, the AAP recommends that parents place their appropriately dressed
infants to sleep on their back, on a firm mattress, covered by a fitted sheet with
nothing else in the crib. Parents should never place an infant to sleep on pillows,
quilts, sheepskins or other soft surfaces. And soft objects, toys and loose bedding
(blankets and comforters) should not be used in an infant’s sleep area.
The purpose of these recommendations is to lower the risk of sudden infant
death syndrome and the unintended suffocation of these infants.
So, what did the study show? In general, potentially hazardous bedding, such as
the objects listed above, are still being used 50 percent of the time when infants are
put down to sleep. That’s right, 50 percent of the time parents still place their
infants to sleep on pillows or quilts or sheepskins, or cover them with blankets and
comforters regardless of sleep location, sleep position, or bed-sharing status.
The study also showed that potentially hazardous bedding is used most often (71
percent of the time) when infants sleep in adult beds and share that bed with others.
Infants of teenage mothers and those with less than a high school education use
potentially hazardous bedding the most (77 percent and 72 percent, respectively.)
Surprisingly, the reasons why parents use potentially hazardous bedding, even
though they have been repeatedly warned not to, are still unknown. And the
number of deaths each year from SIDS remains fairly constant, at approximately
4,000 each year.
THE BABY BEAT – February 4, 2015
Can blue-eyed parents have a child with brown eyes?
So we still have a lot of work to do if we hope to further lower the number of
these tragic deaths.
© 2015 Gary Benfield