Fig. 69. Figure of the chromosome group of an XXY female, that gives non-disjunction.
These four kinds of eggs may be fertilized either by female-producing sperms or
male-producing sperms, as indicated in the diagram (fig. 70).
Fig. 70. Scheme showing the results of fertilizing white bearing eggs (4 kinds) resulting from non-disjunction. The upper half of the diagram gives the results when these eggs are fertilized by normal red bearing, female producing sperm, the lower half by normal, male producing sperm.
If such an XXY female carried white bearing Xs (open X in the figures), and the male
carried a red bearing X (black X in the figures) it will be seen that there should result an exceptional class of sons that are red, and an exceptional class of daughters that are white. Tests of these exceptions show that they behave subsequently in heredity as their composition requires. Other tests may also be made of the other classes of offspring. Bridges has shown that they fulfill all the requirements predicted. Thus a result that seemed in contradiction with the chromosome hypothesis has turned out to give a brilliant confirmation of that theory both genetically and cytologically.
How Many Genetic Factors are there in the Germ-plasm of a Single Individual
In passing I invite your attention to a speculation based on our maps of the chromosomes—a speculation which I must insist does not pretend to be more than a guess but has at least the interest of being the first guess that we have ever been in position to make as to how many factors go towards the makeup of the germ plasm.