PTC Tasting:  Phenylthiocarbamide (PTC) is human-made chemical that is similar to a naturally occurring substance found in turnip greens, brussel sprouts, kale, and other leafy green vegetables. People who can taste this chemical are likely to find the aforementioned plants bitter-tasting and, therefore, unlikely to eat large quantities of these plants. Consumption of large quantities of these plants can increase an individual’s likelihood of suffering from goiter, which is an enlargement of the thyroid. Individuals with at least one dominant allele are able to taste PTC. Since we do not have PTC samples to taste, record your phenotype as taster/dominant if you think turnip greens, brussel sprouts, kale, and mustard greens taste bitter.

Tongue Rolling:  Tongue rolling refers to the ability to roll the sides of one’s tongue upward to create a tube-like shape. Individuals who can roll their tongues have at least one dominant allele for the trait.

Tongue Folding: Tongue folding refers to the ability to fold the tip of one’s tongue backward. Individuals who can fold their tongues have two recessive alleles for the trait.

Earlobe Attachment:  Earlobes are either free-hanging, meaning that the lower boundary of the earlobe dangles away from the neck, or attached, meaning that the lower boundary of the earlobe is connected directly to the neck. Individuals with free-hanging earlobes have at least one dominant allele, while individuals with attached earlobes have two dominant alleles for the trait.


Darwin’s Tubercle:  Darwin’s tubercle is a thickening of the cartilage of the upper-inner rim of the ear. It may be present on one or both ears. Individuals with at least one Darwin’s tubercle have at least one dominant allele for the trait.


Hitchhiker’s Thumb:  The ability to bend the upper joint of the thumb backward more than 50 degrees is referred to as hitchhiker’s thumb. Individuals who have this ability have two recessive alleles for the trait.


Hand Folding:  When one folds his/her two hands together such that the fingers interlock, there is a natural tendency for either the left thumb or the right thumb to be placed on top. Individuals who place the left thumb on top have at least one dominant allele, while individuals who place the right thumb on top have two recessive alleles.

Hair Whorl:  The hair on the top of an individual’s head either whorls in a clockwise (CW) direction or in a counterclockwise (CCW) direction. The former condition is inherited as a dominant, while the latter condition is inherited as a recessive.

Widow’s Peak:  The hairline above the forehead may be roughly horizontal or it may point in a V-shape. The latter phenotype is referred to as widow’s peak and is inherited as a recessive.

Ear Wax:  There are two forms of ear wax in humans. Sticky, yellow ear wax is inherited as a dominant, while dry, gray ear wax is inherited as a recessive.

First, record the sample sizes for the entire class, males only, and females only. (The number of males plus females must equal the total sample size.)

Second, record the total number of individuals exhibiting the dominant phenotype for PTC tasting and convert this into a percentage. Do the same for the recessive phenotype for PTC tasting for the total sample. (To calculate a percentage, divide the number of individuals with the dominant phenotype by the sample size and then multiply that answer by 100. Unless the answer is a whole number, all percentages must be rounded to tenths place.) Repeat for males only and for females only for the PTC trait. Then repeat for the other nine simple traits.

Third, for each trait indicate which phenotype is the most common among the class members.

Fourth, compare the male and female percentages for each trait and indicate which traits exhibit significant phenotypic variation between the sexes. (If the difference between male and female phenotype percentages is greater than 20.0%, consider that a significant difference.)