The Y Chromosome of Drosophila Pseudoobscura.

The variation in the shape of the Y chromosome of Drosophila pseudoobscura Frolowa was first observed by LANCEFIELD (1929). He found that race A of this species has a J-shaped, and race B a V-shaped Y chromosome. This difference in the shape of the Y chromosome remains the only known “morphological” differential between the two races of this species, which are otherwise distinguished by their behavior in crosses (LANCEFIELD, 1. c.), and by a number of physiological characteristics (POULSON 1934, DOBZHANSKY 1935, BOCHE unpublished). DOBZHANSKY and BOCHE (1933) observed that the shape of the Y chromosome does not remain constant even within a race; two types of Y chromosomes occur in race A, and two other types in race B. Further studies, to be reported in the present paper, have increased the number of the types of Y chromosomes known in the species up to a t least six, and shown that each of these types occurs in populations inhabiting a distinct geographic area.