Widow's Peak
Widow's Peak Punnett Square
phenotype
possible genotype
How to inherit a Widow's peak?
Conclusion
Introduction
Origin of the term
It got its name from a myth that if a woman possessed it she would outlive her husband. Though the trait has also been considered a mark of beauty.
The widow's peak trait is a dominant single-gene trait resulting in a V-shaped point in the hairline in the center of the forehead.
The widow's peak gene is called ALX3 and is located on Chromosome 1. A widow's peak is actually a defect in this gene and that defect is then genetically passed down.
Peaks between genders
"A study of women conducted by Nusbaum and Fuentefria in 2009 found that 81% had a widow's peak, but it is unclear what their criteria were in this study; Smith and Cohen's 1973 study on male medical students found that only 3% had widow's peaks, suggesting either high variation between genders or scholarly disagreement over what constitutes a widow's peak." (source: Wikipedia)
In the world
About 35 percent of the world population has a widow's peak.
Age might be a factor
The survey has shown that the presence of a widow's peak in less likely than it's absence, even though the allele for a widow’s peak is the dominant form. Allele frequencies for this trait may not match Mendel's ratios.
Contrary to the results Smith and Cohen found, men should be more likely to have a somewhat "widow's peak." Their hairline recedes over time, and it often recedes slower in the middle. It could therefore be difficult to distinguish between a receding hairline and a true widow's peak in adult men.
source:
"Myths of Human Genetics." Myths of Human Genetics: Widow's Peak. N.p., n.d. Web. 21 Nov. 2016.
The allele for a widow's peak is dominant. Since it is a single-gene trait, a child will display the dominant phenotype as long as one parent has the dominant gene. This means that you are more likely to get a peak than a straight hairline.
The chart represent's a Middle School survey. The majority of students didn't show a visible trait of a widow's peak. (see conclusion)
"Widow's Peak." Wikipedia. Wikimedia Foundation, n.d. Web. 22 Nov. 2016.