The Genetic Factors in the Devi-lopm-n t of the Housemouse, etc. m 



hair of an agouti mouse (ABCDEFGH) is brown, yellow and black, in 

 such a way that the coat presents a ticked appearance. In cinnamon 

 (ABcDEFGH), that part of the hair which in an agouti animal is black 

 is brown, so that the ticking of a cinnamon agouti mouse is much 

 less apparent than that of an agouti one. Just as agouti (.vbcdefgh) 

 is much lighter than black (ABCDEFgH), so is cinnamon (ABcDEFGH) a 

 much lighter colour than ABcDEFgH, chocolate. When the factors B 

 and c are both absent, the difference caused by a presence or absence 

 of G is not nearly so great. The difference between clear orange 

 (ABcDEFGH) (No 24), and Orange (AbcDEFgH) (No 6) is even sometimes 

 difficult to appreciate by one not accustomed to these colours. Where 

 B is absent but c present, the difference caused by presence or absence 

 of G is much more easily seen. Thus it is easy to distinguish yellow 

 agouti (AbCDEFGH) and tortoise (AbCDEFgH) mice, and in rabbits this 

 same difference exists. A tortoise rabbit or mouse is generally darker 

 (sooty) below than above, whereas a yellow agouti is darker on its 

 upper side and has ticked hair. 



In absence of D, the mice having G have a dilute colour, like 

 those without G, in the same circumstances. Where in an agouti 

 mouse or cavy or rabbit the hair is black, it is bluish in the dilute 

 agouti (ABCdEFGH), the yellow parts of the hair become nearly white, 

 and the brown parts become very light brown. In dilute cinnamon 

 agouti (ABcdDEFGH) the colours of the hair are brownish and whiteish 

 and some of the dilute cinnamons are very light in colour. 



Generally speaking are the colours of a cavy darker than tliose 

 of a mouse or rabbit with the same set of colourmodifying factors, 

 thus are especially agouti .abcdefgh, and cinnamon, abcDEFGH darker 

 than agouti or cinnamon mice or rabbits. Matings between animals 

 with and without the factor G have been made in large numbers with 

 cavies by Miss Soll.as and Castle, with rabbits by Castle, Punnett 

 and Hurst. 



In adding the numbers of Gg and gg young from 11 litters of 

 brown rats, from parents of which one was Gg, the other f<g, I find 

 20 Gg and 20 gg ones, exactly the expected ratio. 



With mice, I have added the numbers of young with and without 

 G from hundred litters recorded from parents of which one was hetero- 

 zygous for G (. . . Gg), the other lacking it (. . . gg). They have given: 



212 young Gg and 197 gg, the expected proportion being 

 204.5 •• 204.5. 



