May, 1915.] 
The Chromosome Mechanism 
5i3 
the expression of a character from a specific factor is one which 
presents a marvelous field for investigation and experimentation. 
The influence of the ordinary ecological factors has been studied 
to some extent but not from the exact standpoint of the systematist 
and geneticist. One need only consider the remarkable structures 
developed in certain insect galls to be impressed with the fact, that 
specific characters can be developed without any previous phytog¬ 
eny of the character in relation to the factor being involved. It 
is evident that the same factors may give rise to very diverse types 
of characters, when their immediate environment is changed. 
The influence of the sexual condition and one factor or set of fac¬ 
tors on another may come under the same general category of 
environmental influences determining expression. 
On the hypothesis that the chromosomes contain the heredi¬ 
tary factors, the possible number of gametes and zygote combina¬ 
tions, giving rise to diploid individuals is given below. These results 
must necessarily follow according to the law of chance so long as 
the chromosomes retain their individuality, pair as synaptic mates 
in reduction, and segregate and combine according to the law of 
probablity. 
Let x = number of chromosomes. 
If x = 1 and 2x = 2; 
And chromosomes a ♦ — ♦ n 
( eggs 
Then gametes*, or !• = a n 
[ sperms ! 
Possible combinations = 4. 
aa an na nn 
Hereditary constitutions = 3 
a 2 an n» 
If x = 2 and 2x = 4 
Chromosomes a ♦ ♦ n 
b t — to 
Gametes \ 
eggs 
_ a a 
K ^ 
n n 
K ~ 
, sperms. 
D O 
D O 
Possible combinations 
= 16, as follows 
abab 
aoab 
nbab 
noab 
abao 
aoao 
nbao 
noao 
abnb 
aonb 
nbnb 
nonb 
abno 
aono 
nbno 
nono 
