

3430 LINDSTROM, GENETICAL RESEARCH WITH MAIZE 
dosperm (waxy in this case). This duplication of recessive characters in 
aberrant seeds is never found when the aleurone and endosperm factors 
are not linked. | 
The assumption in these cases is that, in the development of the en- 
dosperm tissue, occasional non-disjunction of the chromosome con- 
taining the linked genes occurs in cell division. The daughter cells of the 
endosperm failing to receive the chromosome with both dominant fac- 
tors develop into areas or spots with the recessive aleurone and endo- 
sperm characters instead of being dominant in those respects. 
LINKAGE GROUPS OF MAIZE: 
Despite the fact that maize has ten pairs of chromosomes there have 
been isolated, by a.tremendous amount of experimental work, at least 
seven groups of linked factors. Such experimental work should provide 
eventuallyaconclusiveargumentfor or against the modern chromosome 
theory of heredity as evolved by the workers with Drosophila. A verifi- 
cation of this theory is certainly necessary in the plant kingdom. 
Historically the first linkage reported in maize was that by COLLINS 
and KEMPTON (1911). It involved the linkage of the factor for waxy 
endosperm and one of the aleurone factors. BREGGER (1918) indentified 
the aleurone factor C as being linked with wx (26.7 per cent crossing 
over). HUTCHISON (1921) added two other factors, sh (shrunken endos- 
perm), and J the inhibiting factor concerned in aleurone color. Factors 
wx and sh gave 21.8 per cent and sh and C 3.4 per cent crossing over. : 
Factors J and Sh giving a crossover percentage of 3.6 suggests that / 
and C occupy the same or very near the same locus. 
The chromosome map of this group can be plotted approximately as 
follows: — . 
Le 3.6 Sh 21:8 Wx 

I. 
ic 25 Wx 
The percentage of crossing-over in maize is somewhat variable and un- 
til further tests are reported the exact location of these factors remains 
somewhat inexact but their relative position is clearly established. By 
means of three-point tests (involving double crossing over) Hutchison 
(1922b) has proven the relative order of these genes to be C — Sh — 
Wx or J — Sh — Wx. 
