CHLOROPHYLL FACTORS OF MAIZE 
Their Distribution on the Chromosomes and Relation to the Problem of 
Inbreeding.! 
E. W. LinpstromM 
Department of Genetics, University of Wisconsin 
T ISasignificant fact that the great 
majority of heritable characters 
known in maize are recessive to the 
normal type in inheritance. Such 
characters as dwarfness, ramosa ear, 
liguleless leaf, chlorophyll characters 
such as white, virescent-white, and yel- 
low seedlings, golden, green-striped, 
Japonica, fine-striped, and the lineate- 
leaved plants are all simple Mendelian 
recessives to the common or normal 
type of maize. Disregarding aleurone, 
pericarp and endosperm characters, 
since one is not certain as to what is 
normal in those respects, only one 
character, pod-corn, has been definitely 
shown to be dominant. Strangely 
enough this dominant character, pod- 
corn, is almost completely sterile in 
the homozygous dominant condition. 
Most of these recessive characters 
influence the life and vigor of the maize 
plant directly. The presence of one 
of them often seriously affects the life 
and productivity of the plant. If any 
such abnormalities were dominant 
characters they would quickly perish 
in the struggle for existence without 
leaving a trace. Because they are re- 
cessive in inheritance they can be car- 
ried along from one generation to the 
next in normal appearing plants, heter- 
ozygous for the abnormal factors. 
This is obviously the reason for the 
presence of so many recessive charac- 
ters and so few dominant ones in maize. 
INFLUENCE OF RECESSIVE CHARACTERS 
The relation between such recessive 
characters and the question of inbreed- 
ing is very intimate. Continued in- 
breeding of maize is nearly always 
followed by a decrease in stature, yield 
and fertility. This, together with the 
facts that the maize plant is normally 
in a heterozygous condition because of 
its method of open-pollination and that 
recessive abnormalities are abundant, 
at once suggests that the artificial in- 
breeding of maize merely isolates the 
recessive characters which are rela- 
tively poor in stature, yield or fertility. 
Having once eliminated these poor 
characters by selective inbreeding, one 
might suppose that the remaining 
plants, being relatively free from such 
abnormalities, would now possess only 
the better characters. This, however, 
is true only to a very limited extent. 
The actual results of maize inbreeding 
have not been successful in producing 
such superior stock. 
Apparently the reason for this is 
the influence of linkage on the distri- 
bution of characters. If one could 
eliminate most of the inferior charac- 
ters without disturbing the favorable 
complex, the problem would be solved. 
But it seems that when we isolate and 
eliminate the poorer types by inbreed- 
ing, at the same time we discard some 
of the better factors that are correlated 
with the unfavorable ones in inheri- 
tance. Such a situation is expected 
from our present knowledge of the 
linkage relations of an organism. 
It seems safe to assume that such 
favorable factors as influence size, 
yield, good quality, and fertility are 
multiple in nature and undoubtedly 
are distributed in all the ten pairs of 
chromosomes in maize. Certainly the 
facts of size inheritance appear to con- 
firm this. 
' Papers from the Department of Genetics, Agricultural Experiment Station, University of 
Wisconsin, No. 22. 
Published with the approval of the Director of the Station. 
Some of the original crosses reported in this article were made at the New York State College 
of Agriculture at Cornell University, Department of Plant Breeding. 
