CORN BREEDING 
JJ 
1 
J 
termine are called allelomorphic characters. There may be any number 
of allelomorphs in a series, but not more than two allelomorphs can 
be present in a single plant. Only two factors are known in the 
japonica series so far, but others may exist and may be discovered 
at any time. If a third should be found, for example /'', there would 
be three possible combinations, namely, J j, J j'\ and j j'\ As only 
two factors of any given pair are present in a fertilized egg cell, the 
j^resence of any one of these combinations prevents the presence of 
either of the others. Several series of such multiple allelomorphs 
are known to exist in corn. For example, B g , B r , r g , r 1 \ and r ch are 
concerned with the development of color in various parts of the 
plant, and any two of them may act as a contrasting pair (22). 
This is known as Mendelian inheritance and is so named in honor 
of the Austrian monk, Gregor Johann Mendel, who first gave us the 
key to its principles. 
Mendel determined 
the inheritance of a 
number of characters 
in the garden pea. 
The same method of 
inheritance has been 
found to obtain for a 
large number of char- 
acters both in plants 
and in animals, and 
it is believed now that 
the principles apply 
to practically all he- 
redity. 
Most cases are more 
complex than the ex- 
ample given. The 
visible characters by 
which inheritance is 
observed generally 
result from the inter- 
action of a number 
of factors that may be inherited independently or otherwise; domi- 
nance frequently is incomplete; a single factor often, if not always, 
affects a number of different characters ; two characters that are indis- 
tinguishable from each other in appearance may be controlled by en- 
tirely different factors ; and, finally, many characters fluctuate widely 
in their expression as a result of environmental and other causes. 
■Jj 
Jj \GR£EMX.SAPOMCA 
i 
J } PEPPODUCT/l/E CELLS 
)P / CPOSSfGPEEU) 
yy\ X JAPO/V/CA 
J j j j\ REPRODJCT/iJE 
7 J CELLS 
J J JJ \PftOGENY PALFGPEEA/, 
J PALFJAPON/CA 
Fig. 3. — Diagram showing the behavior of a single factor 
pair in inheritance. A true-breeding normal green 
strain (J J) is crossed with a japonica-striped strain 
(j ;'). The immediate progeny are normal green (J ;) 
but produce two kinds of reproductive cells J and j, as 
may be shown by crossing back with the japonica 
strain (j j) 
RELATION OF THE CHROMOSOMES TO HEREDITY 
The theory of hereditary factors, as described, was based on evi- 
dence from a large number of inheritance studies in both plants 
and animals. Working from another direction, cytologists had de- 
termined the behavior of the chromosomes in cell division to be as 
has been outlined briefly. The similarity of the processes was so 
evident that the chromosomes immediately were indicated as con- 
