32 AN ANALYSIS OF THE EFFECT OF SELECTION. 
It is evident from these data that Extended is between sepia and 
spineless, some distance from either. It is, then, in the same general 
region as Dichet. 
The lethal effect of Extended has been tested in two ways. Mat- 
ings of Extended by Extended gave 116 Extended to 94 normals. 
If homozygous Extended is viable the result should be 3 : 1; if it 
dies the result should be 2:1. In fact, it was nearer 1:1. This 
result is probably due to the overlapping phenomenon, resulting in the 
classification of some Extended flies as normal. It is suggestive of a 
2:1 ratio, however. More conclusive data was obtained by mating 
heterozygous Extended to Dichet flies heterozygous for lethal III 
(see above), and inbreeding the Extended offspring. If Extended is 
lethal when homozygous, these flies should produce only Extended 
offspring, but these should all be heterozygous. They should, in fact, 
breed exactly like the true-breeding race of Dichets described above. 
This is actually the case. Such a stock has now been kept for four 
months, and is still made up almost entirely of evidently Extended flies; 
but tests show them to be only heterozygous for the character. 
TaBLE 23. 
e 
Spay © Xss3 cS 
Dé | 3e 85 3s | 8s D@| Desg Se N | s D* ss | Total. 
39 | 37 3 3 6 10 a 1 99 
The mating of Dichet x Extended (or vice versa) gave the following 
result: Dichet, 99; Extended, 69; normal, 102; total, 270. If we 
suppose some of the flies classified as ‘‘normal” to be in reality Ex- 
tended, this result approximates to the 1:1:1 expected if Dichet- 
Extended flies die. The fact that the Dichets are only about a third 
of the total shows that half the Dichzt gametes have been eliminated 
somehow. One of the Dichets and a number (4 individual matings 
and 2 mass cultures) of the Extendeds have been tested, and neither 
sort has produced the other. It is, then, safe to conclude that Dichet- 
Extended flies die. 
Culture 1379, in which Extended first appeared, was made up by 
mating together two 8-bristled flies, the male from 1145, the female 
from 1253. The latter culture gave among other offspring 5 sevens 
and 2 eights. The other eight, in 1356, behaved normally, as did 
one of the sevens (in 1857). Culture 1145, however, gave no seven 
and only the single eight. Since 1379 gave a result indicating that one 
parent was Extended instead of 8-bristled Dichet, it seems probable 
that the male parent, from 1145, was the mutant. In either case, 
the Extended parent was produced by mating a 7-bristled Dichst 
As 
