Download HUMAN GENETIC Variability

HUMAN GENETIC Variability
NAME__________________________
PURPOSE:
a) to study the inheritance of some human traits
b) to determine the frequency of selected traits in a given population
c) to see the extent of genetic variability
PROCEDURE:
1.
2.
3.
Read the short description of each of the following traits.
Determine which trait you have (your phenotype).
Record your finding in your Data Table. In recording your genotype, use only a single
symbol to indicate dominance since you do not know whether you are homozygous or
heterozygous for the trait.
a)
Detached/Attached Earlobes: In most people the earlobes hang free (E).
When a person is homozygous for a certain recessive allele (e), the earlobes are
attached directly to the side of the head.
b)
Widow's Peak: In some people the hairline drops downward and forms a
distinct point in the center of the forehead. This is known as a widow's peak. It
results from the action of a certain dominant allele (W)
c)
Tongue Rolling: It used to be thought that a dominant allele (R) gave some
people the ability to roll the tongue into a "U" shape when the tongue is extended
from the mouth. Nonrollers (r) were thought to do no more than produce a slight
downward curve of the tongue. There is current debate about the genetics of
tongue rolling.
d)
Bent Little Finger: A dominant allele (B) causes the last joint of the little
finger to bend inward toward the fourth finger. Lay both hands flat on the table,
relax the muscles, and note whether you have a bent or straight little finger.
e)
PTC Tasting: Place a piece of PTC paper on your tongue. If you detect no
obvious taste, you are a nontaster and are homozygous for a recessive allele (t).
The tasting of this chemical results from the presence of a dominant allele (T).
f)
Finger Hair: Examine the second (middle) joint of each finger for hair. If hair
is present, you have the dominant allele (H).
recessive (h)
4.
5.
6.
If no hair is present, you are
Your teacher will help you gather class data to finish your Data Table.
Now, record your personal genetic information on your Genetic Circle. Put a tally mark
for each of your characteristics, starting with earlobes and moving toward the outside of
the circle. For example if you have attached earlobes you will put a tally mark in “ee” and
then if you have a Widow’s peak you will put another tally mark in the W_ that is right
next to the “ee”. Continue in this way until you have your final tally mark somewhere on
the outside of the circle.
Finally, record your personal genetic information on the Genetic Circle transparency in the
front of the class.
DATA CHART:
Trait
Your
Genotype
Number of
Students
Showing
Dominant
Trait
Number of
Students
Showing
Recessive
Trait
Ratio of
Dominant to
Recessive
Frequency
of Dominant
Trait
Frequency
of Recessive
Trait
Earlobes
Widow’s
Peak
Tongue
Rolling
Bent Little
Finger
PTC Paper
Tasting
Hairy
Mid-Digit
DISCUSSION QUESTIONS:
1. How would it help to extend the outermost section by adding another trait?
2. If you had to keep extending the traits, how many more could you add?
3. Why are there always two choices as you move to each step?
4. If two people ended up on the same outside space, would they look alike? Explain your answer.
5. If you had 100 circles, would two people who ended up on the same outside space look alike?
Explain your answer.
6. To what extent do the ratios obtained compare to Mendelian ratios previously studied?
7. Explain any variation you found in the answer to questions 6.
8. Could two parents who are tasters have a child who is a nontaster? Explain.
9. What situation could result in less variation in a human population than what you have observed?
10. How do the ratios obtained for PTC tasting and tongue rolling compare to the national average?
The national average is 65% for PTC tasting and tongue rolling and 35% for nontasters and
nonrollers.
11. How could you account for variation from the national averages.