

THE INTERACTION BETWEEN TWO CLOSELY 
LINKED LETHALS IN DROSOPHILA AS THE 
CAUSE OF THE APPARENT CONSTANCY 
OF THE MUTANT „SPREAD” BA 
by À. Wine. | 
(Report from the Genetic Laboratory of the Royal Veterinary 
and Agricultural College, Copenhagen). 
/ 
In 1921 I received from Professor ©. Monr, Dr. Sc., Christiania, 
a few cultures of Drosophila melanogaster, among which was the 
mutant spread. During the following months the cultures were 
propagated, however, without it being my intention to examine 
problems regarding this organism which has already been so dili- 
gently investigated from many quarters. But it soon appeared impossi- 
ble to maintain the spread cultures as constant homozygotic lines, 
as now and then single individuals with normal wings turned up 
which, if allowed to propagate, quickly increased the number of 
the normal-winged. As spread individuals on account of their very 
projecting, often dragging wings especially in moist cultures are 
exposed to ruin in greater quantities than those with normal wings, 
this might be instrumental in the latter increasing in number. 
However, the question as to how these normal-winged indivi- 
| duals have arisen was of course in itself a problem. It was not 
probable that it was a question of reverse mutants as they appeared 
several times; I therefore decided to examine the question more 
closely and with this in view I made different crossing experiments. 
When crossing spread with wild type individuals the peculiarity 
at once appeared that segregation always took place as early as 
the Fj-generation, as F, consisted of an equal number of spread 
and normal-winged (to be referred to later). All spread might there- 
fore be supposed to be heterozygotic and spread dominant to 
the normal ones. 
Genetica IV. 21 
