Page 166 - The Evolution Impasse 2

164 Pleiotropic Effect, The

NORMAL DEVELOPMENT PLEIOTROPIC EFFECT
PLEIOTROPIC EFFECT
NORMAL DEVELOPMENT

1- Wings do not
3 en erge.
2- The feet are of
nor mal size, but
their ends fail to
1 de vel op ful ly
3- The is no soft-
4
feath er tis sue.
4,5- The is no lung,
de spite the pres -
5
ence of a res pi a to -
7 ry tract.
6,7- There is no ur -
6
na ry tract and no
way for the kid neys
to de vel op.

2

On the left can be seen nor mal de vel op ment in a do mes tic chick en, and on the right,
the harm ful ef fects caused by a plei o trop ic gene mu ta tion. Close in spec tion shows that
a mu ta tion in a sin gle gene can dam age sev er al or gans at the same time. Even if we were
to ad mit that mu ta tions did have a pos i tive ef fect, the plei o trop ic ef fect would elim i nate
this ad van tage by dam ag ing sev er al dif fer ent or gans at once.

mel a no gas ter, four teen af fect ed the stud ied in high er or gan isms has been
shape of the sex or gans of the fe male, a found to ef fect more than one or gan
char ac ter is tic that one would have sys tem, a mul ti ple ef fect which is
thought was quite un re lat ed to eye col - known as plei ot ro py. As Mayr ar gues
our. Almost ev ery gene that has been in Population, Species and Evolution:

The Evolution Impasse II