PTC Tasting
Frequency: 75% can taste PTC; 25% cannot taste PTC
For some people (and some chimpanzees also), the chemical
PTC tastes very bitter. For others, it is tasteless. PTC is a
harmless compound that tastes bitter to those who have the
most frequent trait. Those with the less frequent trait do not
taste the bitterness.
PTC-like chemicals are found in the Brassica-family of
vegetables, such as cabbages, brussel sprouts, and kale. Some
scientists think that tasters have fewer cavities, suggesting that
there might be a substance in the saliva of tasters that inhibits
the bacteria that cause cavities to form. Others think that PTC
tasting may be in some way connected with thyroid function.
PTC taste was a chance discovery in 1931.
PTC Paper Taster
Copyright 2002, University of Utah
Tongue Rolling
Frequency: 70% can roll their tongue; 30% cannot roll their tongue
Can you roll your tongue into a U-shape? Try it. If you can, then
you possess the most frequent trait. If you can't roll your
tongue, you have the less frequent trait.
In 1940, the famous geneticist Alfred Sturtevant noted that
about 70 percent of people of European ancestry are able to roll
up the edges of the tongue, while the remaining 30 percent are
unable to do so. However, there is some question about the
inheritance of tongue rolling. Recent studies have shown that
around 30% of twins do not share the trait.
Can roll tongue
Cannot roll tongue
Copyright 2002, University of Utah
Attached Earlobes
Frequency: 75% have detached earlobes; 25% have attached earlobes
Have a partner examine your earlobes. If your earlobes hang
free at the bottom, you have the most frequent trait. If they are
attached, you have the less frequent trait.
In most people, earlobes hang free and detached but in some
people the earlobes are attached directly to the side of the head.
The size and appearance of the lobes are also inherited traits.
Detached earlobes
Attached earlobes
Copyright 2002, University of Utah
Hitchhiker’s Thumb
Frequency: 75% do not have hitchhiker’s thumb; 25% have hitchhiker’s
thumb
Try to bend your thumb backwards at the joint. Some people can
form at least a 45 degree angle at the joint. This is called
hitchhiker’s thumb. If you can make a hitchhiker’s thumb you
have the less frequent trait. If your thumb does not bend
backward, you have the most frequent trait.
No hitchhiker’s thumb
Has hitchhikers thumb
Copyright 2002, University of Utah
Cross Left Thumb Over Right
Frequency: 75% are left over right; 25% are right over left
Without thinking about it, fold your hands together by
interlocking your fingers. Which thumb is on top? If the left
thumb is on top, you have the most frequent trait. If the right
thumb is on top, you have the less frequent trait. Try folding your
hands together with the other thumb on top. How does this feel?
Crosses left thumb over right
Crosses right thumb over left
Copyright 2002, University of Utah
Dimples
Frequency: 75% have dimples; 25% do not have dimples
Dimples are a slight natural depression or indentation on the
surface of the cheeks. Dimples are the most frequent trait. If you
don't have dimples, you have the less frequent trait.
Has dimples
Copyright 2002, University of Utah
Hairline
Frequency: 75% have a widow’s peak; 25% do not have a widow’s peak
If you have the most frequent widow’s peak trait you display a
V-shaped point formed by the hair near the top of your
forehead. If you have the less frequent trait, your hairline is
straight.
Has straight hairline
Has widow’s peak
Copyright 2002, University of Utah