Human Biology Kaplan University Week 8 Project

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
genotype.

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.

Procedure

2. 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.

4. Record your findings
   in the Table below (cut and paste the table into a Word document. Save it and
   submit it to the Dropbox).

6. If you show the trait
   write the representative capital in the phenotype space.

8. 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.

10. 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
examples!

2. 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.

4. 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.

6. Detached Earlobes (E)

   The dominant
   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.

8. 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?

10. Hair
    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.

12. 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.

14. Handedness (R)

    The majority (85%) of
    the population is right-handed; the rest are left-handed.

16. 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.

18. 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
    recessive.

20. 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
    recessive.

22. Freckles (F)

    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.

24. Iris
    Pigment (I)

    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
    color.

26. 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.

Questions for
consideration:

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
Traits

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: