Title: Human Genetics- Mendelian Inheritance Name _______________________
Period ______
INTRODUCTION:
Each human is unique. Except for identical twins this difference is due largely to differences in genotype. Each human has approximately 30,000 genes which control his/her characteristics.
The autosomal traits mentioned in this lab are found on one of the first 22 chromosome pairs in the nuclei of each of your cells.
PURPOSE: To investigate the inheritance of human characteristics.
PROCEDURE:
Autosomal Traits.
Use the following information to determine which of the following traits you exhibit. Write your phenotype in the appropriate space and circle your possible genotype(s).
1. The ability to taste the chemical PTC (phenylthiocarbamide) is an inherited
characteristic determined by a dominant gene. This harmless chemical can be
tasted by some people but not by others. Taste a piece of paper that has been
impregnated with PTC. If you detect a bitter taste, you are designated as a taster. If
you detect no taste other than the paper itself, you are known as a nontaster.
Your phenotype ________________________________
Your genotype(s) TT Tt tt
2. A dominant gene determines that earlobes hang free and are not attached directly
to the side of the head. In some people, the earlobe is attached directly to the side
of the head, so that there is no lobe hanging free. The attached earlobe is due to a
recessive allele.
Your phenotype ________________________________
Attached Free
Your genotype(s) FF Ff ff
3. Some people can bend the distal, or end, joint of the thumb back beyond an angle
of 45 o . This is called hitch hikers thumb. Normal thumb angle is dominant and
hitchhiker’s thumb is recessive.
Your phenotype ________________________________
Normal thumb Hitchhiker’s thumb
Your genotype(s) NN Nn nn
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4. Some people have the ability to roll the tongue into a U-shape when the tongue is
extended from the mouth and are known as a roller. This tongue rolling ability is
caused by a dominant allele. People who do not possess this allele can only produce
a slight downward curve of the tongue when it is extended from the mouth and are
known as a non-roller.
Your phenotype ________________________________
Your genotype(s) RR Rr rr
Non-roller Roller
5. Some people exhibit the characteristic of a hairline that comes to a distinct point in
the middle of the forehead. This is known as a widow's peak which results from the
action of a dominant allele. The recessive allele determines the characteristic of a
smooth hairline.
Your phenotype ________________________________
Your genotype(s) WW Ww ww
Smooth Hairline Widow’s Peak
6. Note the length of your big toe in relation to the length of your second toe. The
presence of a dominant allele determines that the big toe is shorter than the second
toe. A recessive allele determines that the big toe is longer than or equal in length to
the second toe.
Your phenotype ________________________________
Your genotype(s) SS Ss ss
7. A dominant allele determines the presence of dimples. A recessive
gene determines the non-dimpled trait.
Your phenotype ________________________________
Nondimpled Dimpled
Your genotype(s) DD Dd dd
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8. A dominant allele determines the presence of freckles. A recessive allele determines
the nonfreckled trait.
Your phenotype ________________________________
Your genotype(s) FF Ff ff
Nonfreckles Freckled
9. Some people have the end of the little finger bent inward. This bent little finger is due
to the presence of a dominant allele. A straight little finger is due to a recessive allele.
To determine if you have the dominant or recessive allele, hold your hands out and
look at the angle of the little finger in relation to your palm.
Your phenotype ________________________________
Your genotype(s) BB Bb bb
10. Note the presence of absence of hair on the middle joints of your fingers. The
presence of mid-digital hair is due to a dominant allele and the absence of mid-
digital hair is due to a recessive allele. Other alleles determine whether hair will grow
on other joints of the fingers and the amount of growth. To observe the hair, hold
your fingers up to the light; some individuals have very light hair on their fingers.
Your phenotype ________________________________
Your genotype(s) MM Mm mm
Absence of Hair Mid-Digital Hair
DISCUSSION:
1. In this lab, how many dominant traits did you show?_____________________________
How many recessive traits did you show?________________________________________
2. If you have more dominant traits than recessive, does this mean you are a stronger
person than someone with more recessive traits?________________________________
Why or why not? _________________________________________________________________
__________________________________________________________________________________
3. A man who was heterozygous for normal thumb angle married a woman who had
hitchhiker’s thumb. Give the genotype of each parent and the chance of them
having a child with hitchhiker’s thumb.
Father's genotype_____________
Mother's genotype___________
Chance of having a child with hitchhiker’s thumb ____________________
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