GENETICS: F. PAYNE 
57 
The high selection line was also mated to black, pink, bent stock. The 
gene for black is in the second, that for pink in the third, and that for bent 
in the fourth chromosome. The Fi flies were mated inter se and the F x 
males were mated back to black, pink, bent females. The normal, the black, 
and the bent flies from these crosses had a much higher bristle number than 
the pink flies. This fact indicated that there probably was a factor for bristle 
number in the third chromosome. To test this possibility the high selection 
line was mated to sepia spineless kidney sooty rough stock. The genes for 
these characters are located in the third chromosome. The Fi females were 
mated to sepia spineless kidney sooty rough males. If crossing-over had 
occurred, this cross should have enabled me to link up the gene for extra 
bristles (if one is present) with one of the other genes. Unfortunately, only 
a low percentage of crossing-over occurs and hence the cross yielded no 
results. 
Another method of analysis was used. A female from the high selection 
line was crossed to a sepia spineless kidney sooty rough male. The Fx 
male from this cross was mated to a sepia spineless kidney sooty rough 
female. The offspring are normal females and males, and sepia spineless 
kidney sooty rough females and males. Some of the normal females and 
males and some of the sepia spineless kidney sooty rough females had 
extra bristles. None of the sepia spineless kidney sooty rough males had 
extra bristles. When the chromosomes of these flies are analyzed, it is found 
that the normal females may get one member of each of the second, third, and 
fourth chromosome pairs from the selection line and must get one of the 
X-chromosomes from this line. The normal males may get one chromosome 
of each of the second, third, and fourth chromosome pairs from the selection 
line, but they get their X-chromosome from the sepia, spineless, kidney, 
sooty, rough line. The sepia spineless kidney sooty rough females get 
both their third chromosomes from the sepia, spineless, kidney sooty rough 
line and may get one member of each of the second and fourth pairs from the 
selection line. They get one X-chromosome from the selection line and one 
from the other. The sepia spineless kidney sooty rough males, however, 
get their X-chromosome and both third chromosomes from the sepia spine- 
less kidney sooty rough line and may get one chromosome of the second and 
fourth pairs from the selection line. Since these sepia spineless kidney sooty 
rough males have no extra bristles, it would seem that the X- and the third 
chromosomes carry the factors for extra bristle number. 
A back selection line started from the eleventh generation and carried for 
twenty-five generations, changed slightly in the first few generations of se- 
lection and then remained practically unchanged. -A mass culture started a 
year ago has not returned to the normal. 
My conclusion then is that there are, at least, two factors for extra bristle 
number and that one of these is located in the first and one in the third chro- 
