Human Genetics – A Sample of Characteristics Controlled by Genes
Introduction:
Genetics is the study of the mechanism of heredity and variation. In other words, it is the study of how
characters are passed on from generation to generation. These characters are expressed differently in
different people due to different gene combinations and environmental conditions, so that each
individual is unique (except for identical twins).
Purpose:
The goal of this lab is to examine a few characteristics that are known to be controlled
by your genes, and determine the presence of certain high frequency traits.
Materials:
Lab handout
Paper Pen
Procedure:
1. Study the following range of characteristics in the human body and then complete the questions that
are at the end of this exercise:
Earlobes
If earlobes hang free, they are detached. If they attach directly to the side of the head, they are attached
earlobes. Some scientists have reported that this trait is due to a single gene, where attached earlobes
is dominant, and detached earlobes are recessive.
(attached / detached)
Bent Little Finger
If you have the dominant gene, your terminal bone of your little finger will bend towards the fourth
(ring) finger. If your little finger is straight, you have the recessive condition.
(bent / straight)
Mid-digital Hair
If you have hair on the middle segment of your fingers, this has been caused by a dominant gene.
(hair / no hair)
Hitchhiker’s Thumb
The technical name for this trait is distal hyper extensibility, but the more common name is hitchhiker’s
thumb. If you have this dominant gene, you can curve your thumb backwards without help, so that it
forms an arc shape.
(curved / straight)
Tongue Roller
Can you roll your tongue into a U-shape, with sides curling upwards? A dominant allele controls this
ability.
(can roll tongue / cannot roll tongue)
Widow’s Peak
You have a dominant allele if your hairline above the brow forms a clear downward point in the center
ofyour forehead. Baldness hides the expression of this gene.
(widow’s peak / straight hairline)
Dimples
If you have dimples in your cheek, a dominant gene controls them.
(dimples / no dimples)
Short Hallux (big toe)
A gene controls the length of the hallux (big toe) relative to the second toe. If your big toe is shorter
than the second toe, you have the dominant gene.
(big toe shorter / big toe longer)
Eye Color
The process of determining eye color is not simple. And it may involve several genes working together.
Any eye color other than pure blue is determined by a dominant allele that codes for the production of
the pigment called melanin. Hazel, green, grey and brown eyes are dominant over blue.
(not blue / blue)
Handedness
The trait of left or right-handedness is genetically determined. You have the dominant allele if you are
right handed.
(right handed / left handed)
Cleft Chin
This trait is reportedly due to a single gene with a cleft chin dominant and a smooth chin recessive.
(cleft / smooth)
Freckles
This trait is reportedly due to a single gene; the presence of freckles is dominant, the absence of freckles
is recessive.
(freckles / no freckles)
2. Complete the table in the following way:
a. For each characteristic listed step 1, write down the allele that you exhibit and whether it is a
dominant or recessive form of the trait. The completed table gives you a record of some features of
your own genetic make-up.
b. As a class we will combine results of the table. Record the results for the class in the chart.
3. Prepare a bar graph that shows the number of people in the class who share the each form of traits
examined. You will have 2 x 12 bars. (we will set up this graph together!)
Questions:
1. What are three of the most common alleles?
2. What are three of the least common alleles?
3. Are there any traits whose frequencies are very similar (close to 50%/50%)
4. Are dominant genes always the most common within a population (do they always have the highest
frequency)? Within the class, are there any recessive alleles that have a higher frequency than
dominant?
5. What is the study of genetics?
6. Explain why different traits are expressed different in different people.
Don’t forget your conclusion!
Results:
Trait
Personal Allele
Dominant or
Recessive?
Total Number in class having
each Allele
DOM
Earlobes
Middle Finger
Mid-Digital
hair
Thumb
Tongue
Hairline
Dimples
Big Toe
Eye Color
Handedness
Cleft Chin
Freckles
Total number in class today: ____________________
Finding Percentage:
REC
%
same as
me