THE LOCATION OF A NEW SECOND 
CHROMOSOME EYE COLOUR GENE 
IN DROSOPHILA MELANOGASTER 
BY GEORG H. M. WAALER 
ANATOMICAL INSTITUTE, CHRISTIANIA UNIVERSITY, NORWAY 

i a back-cross of a single female, heterozygous for the sex-linked 
recessive genes eosin (eye colour), vermilion (eye colour) and 
forked (bristles) to eosin vermilion forked males, there occurred (Oct. 
15, 1919) out of a total of 120 flies 2 females and 4 males having a 
light brownish eye colour, which seemed to differ from all the eye 
colours expected in this test.” These flies were inbred, and for some 
generations selection was carried out in order to get rid of the sex- 
linked genes present, and a stock was obtained which bred true for 
the brownish eye colour mentioned. 
On the assumption that this character, called brown (bw), was 
due to a new mutation, an experiment was carried out in order to 
determine the chromosome to which its gene belonged. Brown fe- 
males were crossed to males heterozygous for the dominant charac- 
ters Star (S) in the second chromosome (at 0,0) and Dichaete (D) in 
the third chromosome (at 385). Both the males and the females ob- 
tained in this cross had wild type red eyes, which proved that the 
gene in question was recessive and not sex-linked. , 
Star Dichaete females from this mating were back-crossed singly 
to brown males (BripGEs and Moraan, 1919, p. 246: the double domin- 
ant test) with the following result: 
S E2750 0b. D bo SbwD  Sbw D + 
261 264 246 308 93 106 126 138 
This’ proved that there was free assortment of Dichaete and 
brown, but seemed to show a coupling to Star, corresponding to an 
amount of 30,0 per cent of crossing over. 
This result would indicate that the locus of brown was in the 
second chromosome about 30 units from Star, and brown flies were 
now made homozygous (concerning the best method of making up a 
