Human Genetics
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    This week you will be examining some rather straightforward human inherited characteristics on yourself.  These are characteristics that are determined by a single gene and provide readily observable phenotypes (the trait which you can see).

    For each of the following nine traits, determine your phenotype (what characteristic you have).  Record your results on the provided tables.  Then determine and record your genotype (or genotypes).

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Attached Earlobes

 

In most people, earlobes hang free (genotype=EE or Ee).  When a person is has 2 copies of the gene for attached earlobes (e), the ears are attached directly onto the side of the head so there are no earlobes.

 

Phenotype Genotype
Unattached Earlobes EE or Ee
Attached Earlobes ee
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Unattached Earlobes Attached Earlobes EE or Ee ee

 

Widow’s Peak

    In some people, the hairline drops down and forms an inverted ‘v’ in the center of the forehead (ala Eddie Munster).  This characteristic is known as Widow’s peak. It results from the action of a certain dominant gene (W). If you have a copy of this gene, you will have a Widow’s peak.

 

Phenotype Genotype
Widow's Peak WW or Ww
No Widow's Peak ww
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Widow's Peak No Widow's Peak WW or Ww ww

 

Tongue Rolling

    A dominant gene (R) gives some people the ability to roll the tongue into a distinct U-shape.  Those who do not possess this gene cannot roll their tongue in this manner. 

 

Phenotype Genotype
Tongue Rolling RR or Rr
No Tongue Rolling rr
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Tongue Rolling No Tongue Rolling RR or Rr rr

 

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 your lab bench and relax your muscles.  Do you have a bent little finger?

 

Phenotype Genotype
Bent Finger BB or Bb
No Bent Finger bb
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Bent Finger No Bent Finger BB or Bb bb

 

Hitchhiker’s Thumb

    This trait is actually known as “Distal Hyperextensibility of the Thumb”, but that is too hard to remember!  This trait is distinguished by the ability to bend the distal joint of the thumb back as far as possible.  Some people can bend their thumb back as far as a 90 degree angle.  It is believed this trait is caused by a recessive gene (h), meaning (2) copies are required to display this characteristic.

 

Phenotype Genotype
No Hitchhiker's Thumb HH or Hh
Hitchhiker's Thumb hh
Now it is your turn... fill this out:
Your Phenotype Your Genotype
No Hitchhiker's Thumb Hitchhiker's Thumb HH or Hh hh

 

Pigmented Iris

    When individuals carry two genes (p) for eye pigmentation, there is no pigment produced in the front part of the eyes resulting in a blue layer at the back of the iris (blue eyes).  A dominant gene (P) causes the production of pigment which is deposited in the front layer and masks the blue to varying degrees.  Other genes determine the exact nature and density of this pigment producing brown, hazel, violet, green and other eye colors.

 

Phenotype Genotype
Pigmented eyes PP or Pp
Nonpigmented eyes (blue) pp
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Pigmented eyes Nonpigmented eyes PP or Pp pp

 

PTC Tasting

    Some persons detect a distinct bitter taste from the obnoxious chemical phenylthiocarbamide (PTC).  Others cannot taste this chemical in small concentrations.  Find the strip of PTC paper in your kit and place it on your tongue.   You will know it if you taste it!  This ‘Tasters’ trait seems to be conferred by having at least one copy of the dominant gene (T).

 

Phenotype Genotype
Taster TT or Tt
Nontaster tt
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Taster Nontaster TT or Tt tt

 

Mid-digital Hair

    Some people have hair on the second (middle) joint of one or more of the fingers while others do not.  The complete absence of hair from this region on all fingers is due to having 2 copies of the recessive gene (m) and having hair is caused by the presence of at least one copy of the dominant gene (M).  There appears to be a number of alleles involved in whether hair growth is on one or more of the digits, but the presence of hair on one digit counts!

 

Phenotype Genotype
Mid-digital Hair MM or Mm
No Mid-digital Hair mm
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Mid-digital Hair No Mid-digital Hair MM or Mm mm

 

Interlocking Fingers

    When your fingers are interlocked between your two hands, some people will always place their left thumb on top while others will always put the right thumb on top.  It is believed that the tendency to place the left over the right is due to a dominant gene (F) while right over left is due to a recessive gene.

 

Phenotype Genotype
Left Over Right FF or Ff
Right over Left ff
Now it is your turn... fill this out:
Your Phenotype Your Genotype
Left Over Right Right over Left FF or Ff ff

 

submit by Tuesday, 2/19, by midnight

 

 

2006 STCC Foundation Press, content by Dawn A. Tamarkin, Ph.D.

Last changed: January 21, 2007