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You Are Special:
A Study of Allelic Frequencies
Name:
Period:
Background Information:
Research of human inheritance has shown that physical characteristics (phenotypes)
are due to variations in the nucleotide sequence in the genotype. Take chromosome
#9 for instance; the offspring of the parental generation (P1) gets one #9 chromosome
from the male and one #9 chromosome from the female to make a pair of #9
chromosomes. That means that all the genes that match up are gene pairs! Each of
the #9 chromosomes code for the expression of many proteins, but one of the gene
pairs code for blood type. The gene pair that codes for blood type is found in the same
location on each of the #9 chromosomes, but the genotype between the two genes will
likely vary. This variation in genetic material, inherited from the P1 generation, is
called an allele. Each allele will express in two distinct phenotypes. The phenotypes
derived from alleles are called traits.
Purpose: To understand and explain allelic variation and frequency.
Prepare to investigate:
1. Study the concept and procedure to fully understand the steps before beginning this activity.
Gather evidence and make predictions:
 Procedure
a) In the chart below you will find 9 different phenotypic traits.
b) Record your phenotype and possible genotype in the chart using 1-9 below as a guide.
c) Two uppercase letters = homozygous dominant
d) Mixed upper and lower case = heterozygous
e) Two lowercase letters = homozygous recessive
f) If you have a dominant trait is recorded as an uppercase letter followed by either another uppercase letter or
a lowercase letter.
g) If you have a recessive trait, you carry two recessive alleles and your genotype is recorded as two lower case
letters (aka homozygous recessive).
Guide (1-9) to filling in the data table below:
1. Widow's peak- When the hairline dips down to a point in the center of the forehead. This condition is caused by a dominant
allele (W), whereas the continuous hairline is from a homozygous recessive genotype (ww).
2. Hitchhikers Thumb- a straight thumb seems to be dominant over a bent one. The letter T is used to express the dominant allele
(straight thumb), a lowercase (t) for Hitchhikers thumb allele.
3. Dimpled chin- a distinct depression or dimple in the chin results from a dominant allele (D).
4. Rolling the tongue- some people can roll their tongue into a hollow straw shape when it is extended. The ability to roll the
tongue results from a dominant allele (R), and the inability to roll the tongue is recessive (r).
5. Hyper mobility of the thumb joints- loose jointedness, or the ability to put the thumb out of the joint, is an inherited
characteristic caused by a dominant allele (H). If you do not show this phenotype then you are homozygous recessive.
6. Bent little finger- laid your hands flat on the table, muscles relaxed. In some people a dominant allele (B) causes the little
fingers to bend toward the ring fingers. Straight little fingers result from a homozygous recessive allele combination.
7. Long palmer muscle- Clench your fist and flex your hand. Now feel the tendons in your wrist. If there are three tendons there,
you have the long palmer muscle, which is a recessive allele (l). The dominant allele (L) only has two tendons.
8. Ear lobes- free ear lobes (E) are dominant over attached ear lobes (e).
9. Mid digital hair- the complete absence of hair in the middle segments of the fingers is a recessive trait (m). Presence of hair on
one or more middle segments of fingers is the result of the dominant allele (M)
Collect the Evidence:
CHARACTERISTIC
CONTINUOUS HAIRLINE
WIDOW'S PEAK
STRAIGHT THUMB
HITCHHIKERS THUMB
DIMPLED CHIN
CHIN NOT DIMPLED
CAN ROLL TONGUE
CAN'T ROLL TONGUE
HYPER-MOBILITY OF THUMB
NORMAL MOBILITY
BENT LITTLE FINGER
STRAIGHT LITTLE FINGER
LONG PALMER MUSCLE
MUSCLE ABSENT
FREE EAR LOBES
ATTACHED EAR LOBES
MID DIGITAL HAIR
ABSENCE OF MID DIGITAL HAIR
PLACE X ON
ROW OF YOUR
PHENOTYPE
LIST OF YOUR POSSIBLE GENOTYPE(S)
Analyze and Interpret the Evidence:
1.
Make a bar graph of the class data.
a. x axis = independent variable (into the experiment) = what was being
observed / studied.
b. y axis = dependent variable (results of experiment) = what were results of
the observation.
2.
If...then… statement (If Independent Variable then Dependent Variable)
3.
Explain the results of the class data (explain which alleles are more frequent).
4.
What connections can be made to class discussions?