Crossing-Over and Chromosome Disjunction

Abstract

DOBZHANSKY¹, Gershenson (above) and others have concluded that the disjunction of chromosomes does not depend directly on the occurrence of crossing-over between them, as I assume to be the case in all homozygous organisms². They maintain that some ” other factor” is concerned in their experiments. But these experiments have necessarily made use of hybridity, without which genetical tests are impossible ; and the particular kind of hybridity (structural hybridity) they have used is bound to have a complicated effect on disjunction. It is itself the ” other factor”. Thus reciprocal crossing-over within two relatively inverted segments should give normal chromosomes with normal disjunction, other things being equal.