5. HEREDITY OF HAIR-LENGTH IN GUINEA-PIGS, AND ITS 

 BEARING ON THE THEORY OF PURE GAMETES. 



By W. E. Castle and Alexander Forbes. 



1. INTRODUCTION. 



In earlier papers (Castle, :o3, :o5) it has been shown by one of us that 

 long or " Angora " coat in guinea-pigs and rabbits is alternative in heredity 

 to normal or short coat. It has been shown further that in cross-breeding 

 normal or short coat dominates over long coat, in conformity with Mendel's 

 law of heredity, but that the purity of the gametes formed by cross-breds 

 is not absolute. Impurity of the gametes is indicated by two facts: First, 

 the number of long-haired young produced by cross-bred parents is in 

 excess of the Mendelian proportion, one-fourth ; secondly, many of these 

 long-haired young show an imperfect development of the long-haired char- 

 acter, as compared with their long-haired ancestors. Both these facts may 

 be explained by supposing that the alternative characters, short and long 

 hair, which are present in the cross-breds — one seen, the other unseen — have 

 in many cases failed to segregate, or have segregated only imperfectly, when 

 gametes have been produced by the cross-breds. Accordingly the con- 

 formity with Mendel's law is a qualified one. 



More extended and detailed studies made by us during the past year 

 confirm these conclusions and add several new facts concerning the behavior 

 in heredity of these alternative characters. The idea advanced tentatively 

 by Castle (:05), that the hair-lengths of guinea-pigs form a discontinuous 

 series of two, three, four or more times the length of short or normal hair, 

 is found to be incorrect. Careful examination of the hair of several hundred 

 guinea-pigs (mostly cross-breds) shows that there occur hairs of practically 

 all lengths from 3.3 cm. up to about 23 cm. The series of supposed maximal 

 hair-lengths of twice 4 cm., thrice 4 cm., etc., resulted from an insufficient 

 number of observations. 



