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GENETICS: C. B. BRIDGES 
Proc. N. A. S. 
heterozygotes, it was found that all the Fi flies that were Diminished were 
at the same time bent or eyeless, respectively. This fact made the intended 
back-cross tests both impossible and unnecessary. Crosses of bent, or of 
eyeless, to wild and to other mutants give only not-bent or not-eyeless prog- 
eny in Fi, while, on the other hand, crosses of Diminished to a great va- 
riety of recessives in the first, second, and third chromosomes have never 
given Fi Diminished that showed any of those recessives. The fact that 
the Diminished allows "pseudo-dominance" of two dissimilar non-allelo- 
morphic fourth-chromosome recessives proves that Diminished is due to 
a fourth-chromosome change, and one of a definite known class — that of 
"deficiencies." 
(9) Pseudo-dominance of recessives in the affected section: Pseudo- 
dominance, such as found for the recessives bent and eyeless with Di- 
minished, had already been met with in such cases as forked with Bar- 
deficiency, 1 vermilion with vermilion-deficiency, 6 and facet, abnormal and 
the white allelomorphs with Notch-deficiencies. 7 The explanation in 
these cases is that the section of chromosome from forked to bar inclusive, 
the section containing the vermilion locus, and the section from white to 
facet and abnormal inclusive, had been lost, or transformed in such a way 
as to have lost the normal action of its genetical materials. All previously 
enumerated features of Diminished are explainable by deficiency for a 
section of the fourth chromosome between and inclusive of the loci for bent 
and eyeless. A diminished individual is virtually haploid for this section. 
The extent of a deficient region is measured in two ways : by observing to 
how many neighboring mapped loci pseudo-dominance extends, and by 
observing the amount by which the map-distance between adjacent not-in- 
cluded loci is decreased in the presence of the deficiency, there being no cross- 
ing over within the deficient region. The Diminished deficiency included 
the only two known fourth-chromosome mutants and thus made the sec- 
ond method impossible in this case. 
(10) Exaggeration of mutants of affected section: The characters bent 
and eyeless in flies that are at the same time Diminished are more exrteme 
departures from the wild-type than are the simple bent and eyeless mutants. 
For example, the legs of the Diminished-bent compounds were much shorter 
and all the tarsi were like those of the hind legs of the most extreme nor- 
mal bents; i.e., they were fused into hairy lumps instead of being chains 
of five slender joints. The eyes of the Diminished-eyeless compounds 
that hatched had about the same range as normal eyeless has ; but among 
the dead pupae were found individuals in which the head was reduced to a 
mere proboscis on the end of the neck. 
(11) Exaggeration of mortality of mutants of affected section: Crosses 
of Diminished to eyeless produced only 35 Diminished-eyeless (all males) 
to 2726 wild-type sibs, where equality is expected. The mortality of eye- 
