HEREDITY IN PLANTS, ANIMALS, AND MAN. 301 
theory lays down is that when gametes are formed by these hybrids with 
the constitution only one of the factors can enter into the same 
Y 
Gt 
gamete, so that we have gametes of two kinds, the first containing the 
Y factor only, the second containing the @ factor only. 
If the gametes from a male and a female individual of these hybrids 
are now allowed to unite together they can do so in four different ways, 
and in four ways only. Amongst a large number coming together by 
chance equal numbers of each combination will result. 
The combinations are + 
: ; ve Hoa 
Y male with Y female, gives Yy original pure yellow pea. 
Yo, Ai tumare 5 Y| yellow pea, because yellow is dom- 
G inant to green, but hybrid in 
constitution. 
G : 
Comes ditto. 
v 
: Gl) a 
original pure green pea. 
G c oO 
We have therefore in the second hybrid generation (F.2.) 
yoy: 2YG 1GG 
that is 1 pure yellow, 2 hybrid yellow, 1 pure green. 
This result agrees exactly with the facts as determined by experiment. 
Mendel’s theory of the purity of the gametes is, therefore, in this case in 
complete accord with the facts. 
We may test it further by seeing the result of crossing a hybrid yellow 
pea with a pure green pea, as illustrated in Diagram 4. 
HYBRID CROSSED WITH RECESSIVE 
ref] 
Pp es © 
Fi Ze. fi] 5 
HYBRIDS AND RECESSIVES 
IN EQUAL NUMBERS. 
DIAGRAM 4, 
The hybrid yellow contains the factors for both yellow and green, its 
Y ; 
, and it produces gametes Y and G in equal numbers. 
G 
constitution being 
