ABSTRACT
By means of X-ray photography the number of lumbar vertebrae was counted in samples of mice from 11 colonies of the C3H inbred strain.
The results confirm Green’s (1953) finding that, of the three main substrains of the C3H strain, one (C3H/He) has predominantly 6 lumbar vertebrae while the other two (C3H/St and C3H/Bi) have predominantly 5 lumbar vertebrae.
In addition, the new data have revealed three factors with significant effects on vertebral variation within substrains of the C3H strain:
A fluctuating variable of the mother’s physiology which affects the prenatal development of the offspring.
A difference between the sexes. The percentage of mice with 5 lumbar vertebrae is higher among males than among females.
Divergences between colonies of the same substrain. The available data are not competent to distinguish the relative contributions to these divergences of nature and nurture.
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