Are the Chromosomes Aggregates of Groups of Physiologically Interdependent Genes?

Abstract

Homozygous translocated types of Drosophila melanogaster differ more or less strikingly from the normal stocks of the same genetic composition in morphology and fertility, while in maize the translocated type is indistinguishable in fertility, size of plant, size of ear, and probably in rate of development. Two explanations for these differences are suggested. (1) In animals, gametes which are more or less defective or unbalanced in their chromosome makeup frequently function in fertilization while corresponding gametes in plants rarely occur on account of the incapacity of the gametophytes, which might produce them, to develop. Possibly in plants, therefore, one obtains in homozygous condition only a highly selected type which does not occasion any significant injury to the organism. (2) Chromosomes may consist of aggregates of groups of genes which are physiologically interdependent. Breaks between groups of genes would not alter the genotype. The case of maize might be of this type. If the chromosome is broken so as to separate the members of a gene group, more or less profound changes in the physiological properties of the complex would follow. The translocations in Drosophila would be of this type.