Download Exercise- .-Human-Genetics

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Name________________________________________________Score_________
Section_______________________________________________Date____________
EXERCISE NO. 6 HUMAN GENETICS
OBJECTIVES
The students should be able to
1. determine the pattern of inheritance of some human traits and abnormalities;
2. arrange chromosomes in correct order to make a karyotype;
3. analyze this karyotype of human chromosomes to identify genetic disorders.
MATERIALS
Family Pedigree
Photographs of C-metaphase human chromosomes spreads (to be given by
instructor)
Filter paper cut into 1 x ½ inch squares
0.5% aqueous PTC solution
PROCEDURE
A. Family Pedigree
1. Submit your family pedigree on a given trait. The pedigree should include your
parents and siblings.
2. With two other family pedigrees of classmates working on the same trait as
yours, copy on your lab manual all three pedigree.
B. Karyotype Analysis
Using a given photograph of human chromosomes, construct a karyotype by cutting
out the chromosomes and arranging them in as nearly matching pairs based on length,
centromeres and satellites (if present)
C. Some Inherited Human Characteristics
a.
Attached Ear Lobes. In most people, the ear lobes hang free, but when a person is
homozygous for a certain recessive gene (e), the ear lobes are attached directly onto the
side of the head so there is no lobe hanging free. By means of a mirror or with the help of
your classmates, determine your phenotype for this characteristic Record results in Table
10-1.
b.
Widows Peak. In some people, the hair line drops downward and forms a distinct
point in the center of the forehead. This is known as the widow’s peak. It results from the
action of a dominant gene (W). Determine your phenotype by examining your front hair
line for a widow’s peak or for a continuous hair line.
c.
Tongue Rolling. A dominant gene ( R ) gives some people the ability to roll the
tongue into a distinct U-shape when the tongue is extended from the mouth. Other, who
do not possess this gene can do no more than produce a slight downward curve of the
tongue when it is extended from the mouth.
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d.
Bent Little Finger. A dominant gene (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 muscle
and note whether you have a bent or straight little finger.
e.
Hitchhiker’s thumb. This characteristic can be determined by bending the
outermost joint of the thumb back as far as possible. Some persons can bend it back until
there is almost (but not quite) a 45o angle between the two joints. Evidence indicates that
this trait is due to a recessive gene. Are both thumbs consistent?
f.
Mid-digital hair. Some people have hair on the second middle joint of the fingers
while others do not. The complete absence of hair from all fingers is due to a recessive
gene (m) and its presence due to a dominant gene (M). This hair may be very fine and you
should use a hand lens and look very carefully on all fingers before deciding on your
phenotype.
g.
Interlocking Fingers. When fingers are interlocked, some people will almost
invariably place the left thumb on top of the right and others will place the right over the
left. Studies indicate that placing of the left over the right is due to a dominant gene (F),
while the right thumb on top is due to a recessive gene (f).
DATA COLLECTED
1.
A. Family Pedigree (Symbolize the probable genotype of each individual in the three
pedigrees.)
STUDENT 1
STUDENT 2
STUDENT 3
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B. Karyotype Analysis
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C. Some Inherited Human Disorders
Table 6-2
OCCURRENCE OF SOME INHERITED HUMAN CHARACTERISTICS
_____________________________________________________________________
Trait
Your Phenotype
Your Genotype
Number in Class
_____________________________________________________________________
Attached Ear Lobes
_____________
_______________
_____________
Free Ear Lobes
_____________
Widow’s Peak
_____________
_______________
_______________
_____________
No Widow’s Peak
_____________
_______________
Tongue-roller
_____________
_______________
_____________
Non-tongue roller
_____________
_______________
Bent Little Finger
_____________
_______________
_____________
Straight Little Finger _____________
_______________
Hitchhiker’s Thumb _____________
_______________
_____________
No Hitchhiker’s Thumb____________
_______________
W/ mid-digital hair
_______________
____________
_____________
No mid-digital hair
_____________
Left thumb on top
_____________
_______________
_______________
_____________
Right thumb on top _____________
_______________
_____________________________________________________________________
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QUESTIONS
2. Based on the family pedigrees, what is the mode of inheritance possible for the trait?
3. From the data collected in Part 6-C, determine if dominance plays a role in the frequency
of appearance of any phenotype. Explain your answer.
4. From the karyotype in Part 6-B, determine if a specific aberration (if any) is involved. Give
the genetic consequences of this anomaly.
5. Research about the following genetic disorders: Tay-Sach’s disease, Thallasemia and
Edward’s Syndrome. Find the cause, type of mutation and characteristics.
6. Do your results show that the ability to taste PTC is an inherited trait? If yes, describe the
mode of transmission of the trait.