If one lumps
together all the cases where any effect of this sort is found, it is
evident that normals never transmit it to their posterity, that affected
persons always do, and that in a mating between a normal and an affected
person, all the offspring will show the abnormality. It is a good
example of a unit character.
But its effect is by no means confined to the fingers. It tends to
affect the entire skeleton, and in a family where one child is markedly
brachydactylous, that child is generally shorter than the others. The
factor for brachydactyly evidently produces its primary effect on the
bones of the hand, but it also produces a secondary effect on all the
bones of the body.
Moreover, it will be found, if a number of brachydactylous persons are
examined, that no two of them are affected to exactly the same degree.
In some cases only one finger will be abnormal; in other cases there
will be a slight effect in all the fingers; in other cases all the
fingers will be highly affected. Why is there such variation in the
results produced by a unit character? Because, presumably, in each
individual there is a different set of modifying factors or else a
variation in the factor. It has been found that an abnormality quite
like brachydactyly is produced by abnormality in the pituitary gland.
Pages:
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182