925
CHAPTER TWENTY-FOUR
Genetics and Genomics
FIGURE 24.7
Previous editions of this (and other) textbooks have used the photograph in (
a
) to illustrate the continuously varying nature
of height. In the photo, taken around 1920, 175 cadets at the Connecticut Agricultural College lined up by height. In 1997, Professor Linda
Strausbaugh asked her genetics students at the school, today the University of Connecticut at Storrs, to re-create the scene (
b
). They did, and
conF
rmed the continuously varying nature of human height. But they also elegantly demonstrated how height increased during the twentieth
century, largely due to improved nutrition. The tallest people in the old photograph (
a
) are 5
9
tall, whereas the tallest people in the more recent
photograph (
b
) are 6
5
tall.
(a)
(b)
Number of dominant alleles
Frequency
0123456
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aabbCC
AaBBcc
AABbCc
AABBCc
aaBbcc
aaBBcc
aaBBCc
AaBBCc
AABbCC
Aabbcc
AAbbcc
AABbcc
AaBbCC
aaBbCc
AabbCC
AABBcc
AabbCc
AAbbCc
AAbbCC
AaBbcc
aaBbCC
AaBbCc
aaBBCC
AaBBCC
AABBCC
FIGURE 24.8
Variations in skin color. A model of three genes, with two alleles each, can explain some of the hues of human skin. In actuality, this
trait likely involves many more than three genes. The mid-range colors are more common.
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