Survey of Simple Human Genetic Traits
Although most human physical traits are coded for by more than one
gene, some are not. These characteristic phenotypes (e.g., height, eye color)
occur because of the products created by a single pair of alleles on each member
of the chromosome pairs you possess.
You will carry two dominant alleles, two recessive alleles or one
of each. If you have at least one dominant allele (commonly notated using
capital letters) for the trait your phenotype is dominant and you will show the
trait. For example, a person who can roll his/her tongue (a dominant trait)
could be either RR (homozygous dominant) or Rr (heterozygous) for the
A person who could not roll his/her tongue would have recessive
alleles (commonly notated using lowercase letters) and would have to have the rr
(homozygous recessive) genotype.
Work with another
person (e.g., family members, friends, coworkers although this works best with
at least one or two family members if possible) to determine your personal
phenotype and possible genotype(s) for each of these human traits.
Record your findings
in the Table below (cut and paste the table into a Word document. Save it and
submit it to the Dropbox).
If you show the trait
write the representative capital in the phenotype space.
If you do not show the
trait write the representative lower case letter in the phenotype space. If you
do not show the trait you can also be certain that your genotype may be a
homozygous recessive condition represented by two small letters (e.g., xx).
Write your genotype for each trait in the space provided.
If you show the trait,
write XX and Xx in the space provided since you do not know for certain which
set of alleles you possess.
Traits…just a few
Tongue Rolling (T)
Tongue rolling is a
dominant trait where the person can roll up the sides of the tongue and make it
tube shaped while sticking it out. Recessive individual’s tongues will remain
flat when extended.
Widow’s Peak (W)
A person with a
Widow’s Peak, the dominant characteristic, will have the hairline across the
forehead come to a V-shaped point approximately in the middle. The recessive
characteristic is a straight hairline with no V-shaped point.
Detached Earlobes (E)
characteristic for this trait occurs when any part of your earlobe is not
connecting to the side of your head. That is, you will have a loop on your
earlobe of any size. People without a loop at the bottom of their earlobes have
the recessive trait; attached earlobes.
Crossing of Thumbs (C)
The crossing of your
thumbs may not seem to be important in the overall scheme of the survival of
mankind but often the products of genes are used for more than one process in
your body (see pleiotropy in the textbook). The product of the gene we see
creating the phenotype of thumb crossing may be important for an as yet
undiscovered body function, which could be crucial for our survival. To do this
test hold your hands out in front of you and interlace your fingers. The
dominant phenotype here is the left thumb being on top of the right thumb. Try
putting your hands together in the opposite fashion, feels weird doesn’t it?
on Mid-digit of Fingers (M)
Hold your hand in
front of you with your fingers sticking straight up. Bend your fingers to that
the middle segment is parallel to the floor (you can lay a dime on your fingers
and it wouldn’t fall off). If there is at least one hair of any size on any of
these middle segments of your fingers you have the dominant trait of mid-digital
hair. If there are no hairs at all you have the recessive characteristic. The
best finger to find the hair on is the ring finger; no we don’t know why.
Hitchhiker’s Thumb (h)
This trait is unusual
because it is named for the recessive characteristic and not the dominant one,
having a straight thumb. For this characteristic you need a nimble thumb and
some loose tendons. Pretend like you were hitchhiking and have your thumb
extended straight up. Bend the top part of the thumb back as far as you can. If
your thumbnail is at a 60° degree angle or more bent out over the rest of your
thumb, you have the Hitchhiker’s Thumb recessive trait. If your thumb doesn’t
bend that far back or you can’t bend the tip of the thumb over your knuckle at
all you possess the dominant trait or straight thumb.
The majority (85%) of
the population is right-handed; the rest are left-handed.
Length of Big Toe vs. Second Toe (S)
Your big toe is also
called your Hallux. If your second toe is longer than your big toe,
congratulations you show the dominant characteristic. A longer Hallux means you
are recessive for this allele.
Facial Dimples on the Cheeks (D)
Smile, that’s what
you’ll need to do to detect this trait. If you have at least one dimple on your
cheeks you possess this dominant phenotype. Having no dimples means you are a
Dimple of the Chin (K)
A family of famous
movie stars is known for their chin dimples. This characteristic is due to the
possession of the dominant allele. If you lack this feature, you are homozygous
These pigmented spots
can show up on just about any part of your body. If you have freckles you
possess at least one dominant allele.
For people who have
blue eyes there is a lack of pigment on the outer layer of your iris and you are
homozygous recessive for this trait. Any color that shows up in your iris other
than blue means that you have at least one dominant allele for eye pigment. The
specific colors of your iris is controlled by other genes, which code for eye
pigments of varying shades of brown, green, hazel, or a combination of colors.
The “I” gene only determines whether your iris will or will not have
Red-Green Visual Deficiency (Red-Green Colorblindness)
The gene for this
trait, unlike the other ones, is located on the X chromosome and is thus said to
be sex-linked Remember that females carry two X
chromosomes and males only one plus one Y chromosome, which has very few genes.
For X chromosomes, alleles are represented by a capital X followed by a
superscript letter for the trait. People with normal color vision, which is
dominant, are either XRXR or XRXr for females or XRY for males. Females who are
recessive and red-green deficient will carry the two recessive alleles, males
will carry only one. Red-green deficient people are represented by XrXr for
females and XrY for males.
Would the person who could roll his/her tongue
know their genotype for certain? Why?
What might determine whether a person who shows
the dominant characteristic is homozygous dominant or heterozygous?
Now, knowing the details of red-green
deficiency, please explain why males tend to show sex-linked traits more often
than females? Can you think of any other sex-linked traits?
Summary of Personal and Class Genetic
|Trait||Possible Phenotype||Sample Size No. of people you tested ||Dominant #||Recessive #||Personal Phenotype||Possible Genotype(s)|
|Tongue Rolling||T or t|
|Widow’s Peak||W or w|
|Detached Earlobes||E or e|
|Thumb Crossing||C or c|
|Mid-digit Hair||M or m|
|Hitchhiker’s Thumb||H or h|
|Handedness||R or r|
|Toe Length||S or s|
|Cheek Dimple||D or d|
|Chin Dimple||K or k|
|Freckles ||F or f|
|Iris Pigment||I or i|
Submitting Your Lab Assignment
Save your copy of the assignment in a location and with a name
that you will remember. Be sure to use the "Save As" option to include your
first and last name in the title of the document. For example, your assignment
might be called Shawn_Edwards_Lab1.doc
When you are ready to submit it, click on the Dropbox and complete
the steps below:
Click the link that
says Submit an Assignment.
In the "Submit to
Basket" menu, select Unit 8: Project 4
In the "Comments"
field, include at least the title of your paper.
Click the Add
Follow the steps
listed to attach your Word document.
To view your graded
work, come back to the Dropbox or go to the Gradebook after your instructor has
evaluated it. Click the Dropbox to access it.
Make sure that you
save a copy of your submitted assignment.