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HUMAN MENDALIAN TRAITS
PURPOSE: This lab will allow students to explore some of their genetic traits. You should be able to
determine your phenotypes, and eventually some of your genotypes for sixteen human single gene traits.
MATERIALS:
Paper and a pencil or pen.
PROCEDURE:
Each member of your group will need to make a table with three columns and
sixteen rows. Head the columns TRAIT, PHENO, and GENO. Down the first column, list the sixteen
traits shown below. In the second column of your chart, you will write yes or no depending on whether
or not you possess each trait. Work with the members of your group so they can help with traits that
you cannot observe directly. In the third column of your chart, record 1st letter of your possible
genotypes using the letters given with each trait. If the letter is recessive, then both will be small (“aa”)
If you possess a dominant trait the genotype could be either homozygous or heterozygous (EX.-"AA"
or "Aa").. When you examine your family you will have a better idea of the both letters of your
genotype, but for now you will need to write 1st letter and a blank (“A_”).
TRAITS:
TONGUE-ROLLING: Have each person to stick out their tongue and see if they can roll the sides up
to form a distinct "U" shape. If you are able to then you possess the dominant gene (R). If you can't,
then you are homozygous for the recessive gene (r).
WIDOW'S PEAK: If the hair line of a person comes down into a distinct point in the center of the
forehead it is because of the presence of the dominant gene (W). If the hairline is straight you are
homozygous for the recessive gene (w).
STRAIGHT LITTLE FINGER: If you examine the "pinky" finger of each person when the hand is
held palm down on the desk, it may form a straight line with the rest of the fingers. If it does it is
because of the presence of the dominant gene (T). If the little finger bends in slightly toward the ring
finger you are homozygous for the recessive gene (t).
STRAIGHT THUMB: This trait is tested by extending the thumb straight up in a hitch hiker's fashion.
If the top segment of the thumb forms a straight line with the bottom segment, it is because of the
presence of the dominant gene (S). If you are able to bend back your thumb so there is a backward
angle in the joint, you are homozygous for the recessive gene(s).
MID-DIGITAL HAIR: If you examine the middle segment of your fingers, you may find hair present.
If it is present, even only 2 or 3 hairs, this indicates the dominant gene (H). If no hair is found, you are
homozygous for the recessive gene (h).
FREE EARLOBES: Examine the earlobes of members of your group. If the earlobes may hang free or they
may be attached directly to the head. If they are hanging free, this indicates the presence of the dominant
gene (F). If they are attached directly to the head, you are homozygous for the recessive gene (f).
LEFT OVER RIGHT INTERLOCKING FINGERS: Hold your hands straight out in front of you.
Now without looking down, clasp your hands together interlocking your fingers. Now look down at
your hands. If your have clasped hands with your left thumb over the right you have the dominant gene
(L). If you are holding right over left, you are homozygous for the recessive gene (l).
CHIN CLEFT: If the center of your chin has a deep indention resembling a deep dimple, you have the
dominant gene (A). If no cleft is present you are homozygous for the recessive gene (a).
INDEX SHORTER: This is a sex-influenced factor which is expressed when the index finger is found
to be shorter than the ring finger. Index finger shorter than ring finger is dominant in the male and
recessive in the female. The dominant letter is (G), the recessive gene is (g).
LONG PALMAR MUSCLE: Have each person clench their fists tightly and flex their hands. Next
examine each of the wrist tendons on the underside of the arm. Count them, if there are three tendons,
it is because of the presence of the dominant gene (P). If there are 3 in both arms, you are homozygous
for the dominant gene (PP). If there are 3 tendons in only one arm, you are heterozygous (Pp). If there
are only 2 tendons in both arms, you are homozygous for the recessive gene (pp).
DIMPLES: If you have a dimple when you smile in either cheek you possess the dominant gene (D).
No dimples means you are homozygous for the recessive gene (d).
SECOND TOE LONGER: If your second toe is longer than your big toe you have the dominant gene
(B). If it is shorter, you are homozygous for the recessive gene (b). An old "wives tale" says that if you
have this trait you will run your family.
CONVEX NOSE: If your nose curves down with a slight "hump" in it you have a convex nose with
the dominant gene (Q). If your nose is straight or curves up, you are homozygous recessive (q).
SIX-FINGERS: This is a fairly rare trait. If you were born with six fingers you have the dominant
gene (M). Five fingers means you are homozygous recessive (m). Often, the doctor will cut the sixth
finger off at birth, sometimes even the mother never knows.
NATURAL KINKY HAIR: If your hair is naturally kinky , you have the dominant gene (N). All other
types of hair are recessive (n).
FRECKLES: If you have freckles you have the dominant gene (Z). If you have no freckles, you have
the recessive gene (z).
BROAD NOSE: If you have a broad nose, you have the dominant gene (J). If you have a narrow nose,
you have the recessive gene (j).
WHITE STREAK: If you have a white streak through your hair, you have the dominant gene (X). If
you have normal hair color you have the recessive gene (x).
NEARSIGHTEDNESS: If you are nearsighted (you can see up close, but need glasses to see in the
distance) you have the dominant gene (C). If you have normal vision, you have the recessive gene (c).
BROAD LIPS: If you have broad, full lips you have the dominant gene (I). If you have thin lips you
have the recessive gene (i).
MIGRAINE HEADACHES: If you have migraine headaches, you have the dominant gene (U). If you
don't then you have the recessive gene (u).
LARGE EYES: If you have large eyes, you have the dominant gene (V). If you have small eyes, you
have the recessive gene (v).
TASTE PTC: If you can taste the PTC in test papers, you have the dominant gene (E). If not, you are
homozygous recessive (e). This gene can affect the types of foods we like. We always assume that
everyone else "tastes" like we do, but they don't.