GENETIC VARIATIONS IN HAND SPAN SIZE

RICHARD CHILTON                CHICAGO VOCATIONAL HIGH SCHOOL
                               2100 EAST 87TH STREET
                               CHICAGO, IL
                               1-312-978-1600

OBJECTIVE:
Students shall measure their handspan size to determine if one pair or many 
pairs of genes control that trait.


MATERIALS:
Metric rulers, Basketball, Lab. Worksheet, Graph paper, and Graphic 
overlays.


STRATEGIES:
Obtain a metric ruler, lab. worksheet and graph paper. Measure your 
handspan size as demonstrated by teacher, spreading out your hand on a 
sheet of paper.  Draw a line from the tip of your thumb to the tip of your 
little finger.  Do not include length of fingernails.  Measure the length 
of the line (your handspan)  in millimeters.  Record the measurements of 
all members of your class on the chalkboard. Organize the measurements into 
a graph showing handspan size  in groups of 5 mm. Also record the number of 
students in each group. Draw a graph of the data in the table. Then carry 
Basketball out to students to see if students can place handspan across the 
Basketball and hold in place without touching any object. Next, answer the 
following questions:  

 
(1) What does the graph reveal about the differences in handspans within 
your class?

(2) Based upon these data, do you think size of handspan size is 
controlled by one or more pairs of genes?

(3) What other factors can affect hand size?

Conclusion:  If a genetic trait is controlled by a single pair of genes, 
then class results would usually show only two categories or groups. When a 
genetic trait is controlled by several pairs of genes, a number of 
different groups will appear. Therefore, this genetic trait must be 
controlled by more than one pair of genes.