OLD TYPES AND NEW 



167 



these hybrid young four varieties are obtained in 

 the next generation, viz., black, brown, bhick-eyed 

 yellow, and brown-eyed yellow, the latter a variety 

 unknown before Castle's experiment in breeding 

 was made. 



For the sake of clearness the formation of the 

 brown-eyed yellow is shown below in Figure 50. 



cT Y^ 



V 



Be 



V 



bE 



be 



S^ 



BE 



BE 



Black 



5 



Be|]BE 



Black 



bE| BE 



Black 



13 



BE 



b G 



Black 



V 



Be 



^ 



BE 



Be 



Black 



6 



Be Be 



Bfack-eijed Yellow 



JO 



bE B© 



Black 



14 



be 



B 



Black-eHed Yellow 



\y 



be 



3 



BE 



bE 



Black 



7 



Be bE 



Black 



I] 



bEllbE 



Chocolate 



4 



BE 



be 



Black 



8 



B 



e 



be 



Black -eHedYellovj 



12 



bE be 



Chocolate 



15 16 



be bE be be 



Chocolate Brown-e\jed Yellow 



Fig. 50. — Diagram to illustrate the origin of a brown-eyed yellow guinea- 

 pig from two heterozygous black parents based upon Castle's experi- 

 ments. The factor for yellow (F) is present in every gamete and is 

 consequently duplex in every zygote but is hidden whenever the fac- 

 tor B is present. B, black pigment hiding brown or chocolate ; h, 

 chocolate (absence of B) ; E, extension of B over the entire body 

 hiding Y ; e, restriction of B to eyes alone thus exposing Y over the 

 entire body. 



