A straight hairline follows the top edge of the forehead without any dips or bends. This is the opposite of a widow’s peak hairline, which generally features a sharp point near the center of the hairline along the forehead. The straight allele is a recessive gene, meaning those with these hairlines must have two parents with the same recessive gene to inherit one.
For most people, having a straight hairline versus a widow’s peak makes little difference in their lives. Straight hairlines aren’t usually more difficult to style than widow’s peak hairlines, and neither hairline appears to be linked to baldness. The interesting thing about having this hairline is where it came from. Two people with widow’s peaks, or the dominant trait, may still have a child that shows the recessive. This child may also possess a recessive hair or eye color because these traits sometimes travel in clumps.
When assessing how genetic traits, or alleles, are passed down, scientists often assign them a letter. In this case, the dominant allele, a widow’s peak, is given the letter W. This allele is given a lowercase w because it is the recessive trait of the same gene. Two parents with widow’s peaks must each carry a recessive allele in order for any of their children to inherit a straight hairline. For instance, two parents with a genetic combination of Ww, who have four children, will likely have one child with a straight hairline.
The other three children in the above family will probably inherit WW, Ww, and Ww alleles, respectively. This means that two children have the potential to pass on the straight hairline gene, while one child does not. Say the child with the WW alleles reproduces with someone that has ww alleles. All of this couple’s children will have Ww genes, meaning the recessive gene will only show up in their grandchildren.
Though many people carry a combination of two dominant hairline alleles, the Ww combination, with one recessive allele, is often the most common combination. If someone with a hidden straight hairline allele reproduces with someone possessing ww alleles, their children are very likely to have straight hairlines. In fact, if that couple has four children, two of them will probably show this recessive gene. The other two children have combination alleles, meaning they could pass either kind of hairline on to the next generation.