24 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



ALBINISM AND LATENT PIGMENT CHARACTERS. 



Although, as we have seen, (i) albinism is a condition recessive in 

 heredity with respect to ordinary or centripetal pigmentation, and (2) 

 albinos produce only albino offspring, irrespective of their ancestry, it 

 is not true, as might be supposed, that one albino breeds like another 

 when crossed with the same centripetally pigmented type. This mat- 

 ter has been very fully discussed by Allen ( : 04, p. 130), but may be 

 illustrated by some simple examples. (i) My albino guinea-pig, 

 cf 2002, when mated with red females, invariably produces offspring 

 marked with black as well as with red pigment. (2) Albino cf 635, 

 when mated with the very same or with similar red females, produces 

 young about half of which are pigmented with black and red,- like the 

 offspring of ^ 2002, the other half being pigmented only with red or 

 yellow, not with black. (3) Albino tf 1999* when mated with red 

 females, produces only red (or yellow) pigmented offspring, never 

 black pigmented ones. From an inspection of these three albino males 

 or of their offspring by albino females, one would get no inkling of the 

 existence among them of the differences revealed by the experiment 

 described. This experiment shows that in the gametes produced by 

 $ 2002, the capacity to form black pigment is latent. This capacity is 

 exercised whenever such a gamete unites with one bearing the centri- 

 petal type of pigmentation. In $ 635 only about half the gametes 

 formed contain latent black; in $ X 999 none of the gametes formed 

 contain latent black. The idea underlying this explanation is that a 

 recessive character (in this case albinism) may contain the dominant 

 one (centripetal pigmentation) in a state of inactivity which nothing 

 but cross-breeding with the pigmented type will disturb. Further evi- 

 dence in support of this idea will be adduced when we come to discuss 

 coat characters other than those of pigmentation. 



Meanwhile, let me say a word concerning the term latency. In com- 

 mon with others I have frequently in earlier papers used this word 

 loosely as synonymous with recessive. This usage was, I believe, an 

 unfortunate one ; accordingly, in what follows I shall use the two 

 terms for conditions quite distinct, which my experiments show to 

 have a real existence and to require names, (i) Recessive I shall 

 use as Mendel used it, to designate a character which disappears when 

 brought by fertilization into the same (hybrid) individual with a con- 

 trasted " dominant" character, but which is transmitted, distinct from 

 the dominant character, in half of the gametes formed by the hybrid 

 individual. (2) Latency, as I shall use it, is a condition of inactivity 

 in which a normally dominant character may exist in a recessive indi- 

 vidual or gamete. It is questionable whether a recessive character 



