LINKAGE IN EATS 1 



HEMAN L. IBSEN 

 Kansas State Agricultural College 



At the present time there are at least five factor pairs 

 or series known in rats. Some of these have been de- 

 scribed only quite recently, and it may therefore be prof- 

 itable to tabulate all of them and to mention some of their 

 interactions. 



These genes are : 



1. R, black-eyed; r, red-eyed. 



2. P, black-eyed ; p, pink-eyed. 



3. S, self; St, Irish; S>, hooded. 



4. A, agouti; a, non-agouti. 



5. C, intense pigmentation; non-yellow; Cn, albinism. 

 Color varieties homozygous for one or the other of the 



first two recessive genes mentioned above were described 

 by Castle (1914). Both are yellow-coated. A PPrr ani- 

 mal is yellow with eyes of a reddish tint, while animals of 

 the composition ppRR or pprr are yellow with pink eyes. 

 Pink-eyed yellows, therefore, may be of two kinds, those 

 carrying B and those lacking it. Animals carrying both 

 P and R are black-eyed and have black coats. Pink-eyed 

 yellows, carrying R (ppRR), mated to red-eyed (PPrr) 

 produce PpRr, black-eyed animals having black coats. 

 Pink-eyed yellows lacking R, and therefore of the compo- 

 sition pprr, when mated to red-eyed yellows (PPrr) give 

 Pp rr, or red-eyed yellows. 



Castle and Wright (1915) and Castle (1916) present 

 evidence that the genes above described are linked. When 

 pink-eyed yellows (ppRR) were crossed with red-eyed 



