Concepts of Biology (BIOL115) - Dr. S.G. Saupe (ssaupe@csbsju.edu); Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321

Single Gene Traits in Humans 

    The following is a list of some autosomal human traits that have been attributed to a single gene.  Although clearly other genes are involved, the inheritance of each of these phenotypic traits acts as if it were governed by a single gene.  First, indicate your expression of the trait (i.e., circle the appropriate phenotype).  Then, indicate if you exhibit the dominant or recessive trait (D or R?).  Finally, using any letters/symbols you want, write your genotype for the trait (hint:  if you show the recessive trait, your genotype will be homozygous recessive (i.e., "aa").  If you exhibit the dominant trait your genotype could be homozygous dominant (i.e., "AA") or heterozygous (i.e., "Aa").  A shorthand symbol for this is "A_").  How could you distinguish between these possibilities? 

Trait

Phenotype

Dominant or recessive phenotype?

Genotype

Tongue Rolling (Dominant)

roll/not roll

 

 

Widow's Peak (D) - just like Eddie Munster

yes/no

 

 

Wet ear wax (D) - stick your finger in to check

wet/dry

 

 

L/R interlocking finger (D) - without thinking, clasp your hands together, is the right thumb over the left, or vice versa?

L/R or R/L

 

 

Attached earlobes (D) - ask a neighbor or check out the mirror

yes/no

 

 

Hitchhiker Thumb (r) - does it bend back at a 90 angle

yes/no

 

 

PTC tasting (D) - I'll have some test paper in class

yes/no

 

 

Chin fissure (D) - like actor Michael Douglas

yes/no

 

 

Darwin tubercle (D) - little bump on the inside of the ear

yes/no

 

 

S-methylthioester detection (Recessive) - can you smell asparagus odor in urine?

yes/no

 

 

Pigmented iris (D) - any color but blue

yes/no

 

 

Freckles (D)

yes/no

 

 

Polydactyl (D) - more than five fingers and/or toes

yes/no

 

 

Dimples (D)

yes/no

 

 

Wooly hair (R)

yes/no

 

 

Long eyelashes (> 1cm; D)

yes/no

 

 

Short big toe (D) - the big toe is shorter than your second one

yes/no

 

 

 

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Last updated: July 14, 2009     Copyright by SG Saupe