Expert: Florence M Rollwagen - 2/11/2009

Question
As a student in a high school biology class, we are covering basic genetics.
While we learned of punnet squates and such, we went over the appearance
of a widow's peak in a person. I know that the widows peak is a dominant
gene, but both of my parents do not have widows peaks. So i know that in
order for that to happen, both parents must be double recessive (ww). I
however, have a widows peak. Im very very sure that the parents i have now
are my real parents. So my question would be, is it possible for a dominant
trait to come up from two recessive ones?


Answer
Hi Morgan:  Thanks for your question.

When we teach introductory genetics, we like to stick to black-and-white genetic inheritance.  Alas, there usually is no such thing.

As you have already found, widow’s peak inheritance is not an either-or condition, although in most cases it is.

There are a number of conditions that will give a person a widow’s peak, with Aarskog syndrome, widow’s peak syndrome and Opitz syndrome being the most common.

However, I think it’s more likely that actual hairlines are controlled by multiple genes (think of baldness variability).  So the effect of the widow’s peak (W) allele can be changed by the occurrence of multiple other genes.  This phenomenon is called epistasis.

Evidence for this can be seen in the fact that people have different variability in widow’s peak.  Some are deeper, some are shallower.

The reason that science can’t really answer this is that science is funding driven.  Money is given to research actual genetic diseases, with potential payoff in life extension.  Because widow’s peak is not a lethal condition, nobody really studies it at the genetic level.

I know this isn’t the answer you were hoping for, but it’s the best I have at the moment.  Who knows?  You may develop an interest in genetics and study the problem yourself!

Write back if you have more questions.


FM Rollwagen, PhD