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Tips on Scoring Genetic Traits

These traits are thought to be determined by single genes and have a dominant and recessive form: Tongue Rolling, Widow's Peak, Dimples, Cleft Chin, Earlobe Attachment, Finger Hair, and PTC Tasting. Scoring these traits is fairly unambiguous and information to help you is given below. Inexpensive biophoto sheets containing color photographs of a number of common genetic traits are available from Carolina Biological (see below). Some traits on the sheets are more difficult to score.

Tongue Rolling. The ability to roll your tongue upwards to form a closed tube. The sides of your tongue will meet at the top of the tube if you can roll your tongue. When students first learn tongue rolling is an inherited trait, they may be surprised and comment that if only people who can't roll their tongues would practice, they could learn to roll their tongues too. Tongue rolling, then, is an example of a "motor skill" that is inherited. Is a good golf swing or a good free throw shot any different?

Widow's Peak. If you have Widow's Peak, your forehead hairline will have a downward dip in it, as in a heart. Lift up the hair of your forehead to score this trait. People without widow's peak have a smooth hairline with no dip. Men starting to go bald (or already bald) may be unable to score this trait.

Dimples. Indentations in the cheeks, especially noticeable when smiling. Score as "yes" only if a dimple on each side is present. Score those with a dimple on only one side as "no."

Cleft Chin. A dimple or cleft in the center of the chin. Famous examples: John Travolta, Kirk Douglas.

Earlobe attachment. Earlobes are attached if the bottom lobe is attached directly to the head. Earlobes are free if the lobe hangs free.

Finger Hair. Officially known as Mid-digital Finger Hair. Consider your fingers to have 3 segments, top, middle, and bottom. If hair is present on the middle segment of any finger, even just one hair, you have mid-digital hair. Do not score the bottom segment of your fingers for hair, just the middle segment. Look closely, as is can be difficult to score. Hair may be present on only one finger or very fair, especially in children..

PTC Tasting. The ability to taste the chemical PTC, which is harmless when ingested in small amounts. To a non-taster, the PTC has no taste. Paper strips impregnated with small amounts of PTC are available from several sources (see below).

Traits difficult to score. We do not recommend scoring bent little finger (frequently ambiguous), short index finger (not immediately observable; requires a mathematical formula), or short hallux (the grossness factor of having students ake off their shoes and socks in class).

Supply Information

Human Phenotypes Biophoto Sheet 1. Pad of 30 sheets with color photos of earlobes, widow's peak, tongue rolling, hithhiker's thumb, and bent little finger. Cost: $7.95. Order RG-17-4831 from Carolina (800-334-5551).

Human Phenotypes Biophoto Sheet 2. Pad of 30 sheets with color photos of mid-digital finger hair, dimples, short hallux, short index finger. Cost: $7.95. Order RG-17-4831 from Carolina (800-334-5551).

PTC Paper Strips.
Carolina RG-17-4010. Cost per 100 strips: $3.60. (800-334-5551)
Flinn Scientific AP7989. Cost per 100 strips: $1.02. (800-452-1261). We like the "format" of the Flinn strips.
Ward's 14W4105. Cost per 100 strips: $1.05. (800-962-2660).