Interspecific Sterility

Abstract

DR. BATESON in his letter on interspecific sterility (NATURE, July 15, p. 76) seems to lay insufficient emphasis on certain facts. If one considers plant and animal species in general, it would appear that interspecific sterility is by no means so general as was formerly assumed to be the case. Among the Œnotheras, in which great numbers of species crosses have been made, complete fertility, in the sense that large numbers of fertile offspring are produced, is the rule unless the forms differ in chromosome number. Even species of Œnothera which come from widely separated regions and differ conspicuously in all their characters, including flower-size, are fertile in crosses. That a certain amount of gametic and zygotic sterility also frequently occurs is of course well known, and it is probably correctly interpreted in terms of lethal factors. But lethal factors are not peculiar to wild species, for numbers of them arise in the mutations of Drosophila melanogaster.