CHAPTER V 



HEREDITY OF COLOUR CONTINUED. 



Albinos giving Coloured Offspring; Reversion on Crossing 

 Various Kinds of Whites Stocks Orchids Pigeons 

 Fowls Primula. 



WE have seen that albinos, both animal and vegetable, 

 though devoid of pigments, may yet bear factors which are 

 capable of determining the quality and distribution of colour 

 when they meet with colour in the zygote. Particular 

 colours may thus be due to the co-existence of several 

 distinct determining factors, each with an independent 

 distribution among the germ-cells. The grey of the rabbit 

 for instance is caused by the presence (i) of a colour- 

 element or elements ; (2) of a factor which determines them 

 to be the mixture we call grey, and not for instance, black 

 or yellow. In the case of certain plants this analysis can 

 be carried a step further, and the formation of colour at all 

 in the flowers can be proved to depend on the co-existence 

 of two complementary factors in the individual. 



The first indication of this phenomenon was found in the 

 fact that two plants each totally devoid of colour in the 

 flowers and stems, and each breeding true to albinism, may 

 when crossed together give purple flowers in F v The two 

 white parents each contain a factor which, alone, is incap- 

 able of forming colour. Each of these factors is indepen- 

 dently transmitted in gametogenesis, and thus in F^ the 

 ratio of coloured individuals to whites is 9 : 7. This pro- 

 portion depends on the fact that a series of 16 individuals 

 is necessary to exhibit all the possible combinations of 

 germ-cells, for, as in any example of hybridisation involving 

 two pairs of allelomorphs, there will be lour types of female 

 cell and four types of male cell produced by F v Of these 



