Robertson's law
/ˈrɒbəts(ə)nz ˌlɔː/Genetics
noun
An empirical law stating that the number of chromosome arms of a population or species tends to remain constant, although the number of chromosomes may vary.
Origin
1930s; earliest use found in Proceedings of the Zoological Society of London. From the genitive of the name of William R. B. Robertson + law.