Expectations on Random Occurrence of Structural Interchanges between Homologous and between Non-Homologous Chromosomes

Abstract

On the assumption that the breakages and recombinations occur at random, a generalized expression, 4(N-1):1, is derived for calculating in any given organism the expected ratio of 2 viable chromosomal interchange types, viz., the one between the non-homologues resulting in a ring at meiosis and the other between the homologues resulting in a pair of pseudo-isochromosomes. The theoretical ratio for these 2 interchange types can be obtained by substituting the number of chromosome pairs of the species studied instead of N in the ratio. Results from the 8 comparisons of the observed data from barley and maize grown from seed treated with various types of radiation with the theoretical, except in 2 cases, indicate that the interchanges between chromosomes, non-homologous or homologous, are random.