An Introduction to a Biology 



II 



At a time wKen I did not clearly see this relation, I had 

 before me some data which convinced me that the Men- 

 dehan interpretation of the phenomenon of segregation was 

 wrong, and that the facts were striking evidence of the 

 truth of Galton's theory. 



There are two attributes of a heterozygote which are 

 said to follow from the theoretical constitution of its gonad ; 

 one is that a quarter of the population produced by the 

 union of heterozygotes consists of individuals bearing the 

 recessive character, and the other is that half the population 

 produced by mating heterozygotes with recessives consists 

 of recessives. My hybrids ^ were tested for these two pro- 

 perties and the results were not denied to be in accord with 

 Mendehan expectation. But this result was not conclusive 

 in favour of that theory only, because the proportion of 

 recessives demanded by Mendelian theory in the case of the 

 first property was identical, and in the case of the second 

 only slightly less than that which follows from the truth 

 of Galton's generalisation. ^ 



The Galtonian prediction of the number of albinos that 

 will be produced by two hybrids (H), each of which is the 

 offspring of a pure-bred waltzing and a pure-bred albino 

 mouse, is -25 of their generation ; while on that theory the 

 proportion of albinos in a generation resulting from the 

 union of hybrids with albinos {A) is -53125, if we only calcu- 

 late as far back as the great-grandparental generation. 



We have seen, therefore, that hybrids were mated with 

 hybrids, and that they were also mated mth albinos. In 

 this way two kinds of hybrids were produced which could 

 not be distinguished from one another by their outward 

 appearance, but differed in the amount of their albino an- 

 cestry ; for while the one kind, which we may call HH, 

 resulted from the union of two hybrids, the other, HA, 



1 Biometrika, Vol. 3, pp. 30-33. 



2 Francis Galton, " Proc. Roy. Soc," Vol. 61, p. 402, line 13. 



147 



