8 



INHERITANCE OF COAT-PIGMENTS AND COAT-PATTERNS 



was recessive, have produced 201 albinos to 244 pigmented young, or 45.1 

 per cent albinos, where 50 per cent are expected. The deviation of nearly 

 5 per cent from expectation in the latter case is probably a matter of chance 

 and would grow less with more extensive observations, for in studying the 

 inheritance of total albinism some observers record an excess of albinos 

 (Castle, 105), others an excess of pigmented individuals (Allen, 104), while 

 others observe very close agreement with expectation (Cu^not, Darbishire). 

 This is as we should expect on the theory of probabilities (see Allen, 104, p. 82). 



LATENT PIGMENT CHARACTERS AND COAT-PATTERNS. 



Latent transmission of pigment characters through albinos is a matter 

 requiring fuller consideration. Assuming for the time being its correctness, 

 and knowing the well-established facts, (i) that gray pigmentation in rats 

 is dominant over black (Crampe, Bateson, Doncaster) and (2) that every 

 sort of pigmentation is dominant over albinism, we reach the following 

 conclusion. On Mendelian principles we may expect partial albinos to fall 

 into eighteen actually different classes, though visibly the classes number 

 only four, namely, gray Irish, black Irish, gray hooded, and black hooded. 

 These eighteen classes are enumerated in the four central columns of table i, 

 page 34. Of gray Irish individuals, there should be eight actually different 

 classes as regards gametic output; of black Irish and gray hooded indi- 

 viduals, there should be four classes each; and of black hooded, two classes. 



Albinos, though indistinguishable in appearance, should fall into nine 

 different classes as regards the latent pigment characters and color-patterns 

 which they transmit. The nature of these nine classes is indicated in the 

 last column of table i. The numerals prefixed to the class designations in 

 table i indicate the frequencies in which the various classes may be expected 

 to occur as a result of a particular sort of mating, namely, mating inter se 

 gray Irish individuals which bear recessive the three characters, total albin- 

 ism, black pigmentation, and hooded pattern, individuals designated 

 GI(W.BH). The table is based on the assumption that gray Irish indi- 

 viduals of the sort indicated are Mendelian triple heterozygotes, the three 

 independent pairs of allelomorphic characters being pigmentation versus 

 albinism, gray versus black, and Irish versus hooded. In support of the 

 assumption mentioned, it may be said that by proper breeding tests a majority 

 of the hypothetical classes have been shown to exist. Thus, of the eighteen 

 hypothetical pigmented classes enumerated in table i, all except four have 

 been shown to occur, those four being GI(W), GI(BH)* BI,* and BI(W)*. 

 Further, five out of the nine supposed classes of albinos have been proved 



* Demonstrated to exist since the foregoing was written. 



