Types of Comb in Fowls. — Five types of comb in 

 fowls exist, viz., the single (found in wild jungle fowl) the 

 rose, the pea, the walnut, and the breda. Crossing the 

 types gives the following results which are explained by 

 Batesonand Punnett on the assumption that the Rose comb 

 is due to the presence of a factor R dominant to an absence 

 r, and the Pea comb to an independent factor P dominant to 

 an ab sence factor p. When both R and P factors are pre- 

 sent in the cells of the zygote a Walnut comb is produced , 

 and when r and p, their recessives or absences, a Single comb 

 results. For example the genetic formula RRPP, RrPp or 

 RrPP represents a walnut comb, RRpp or Rrpp a rose, 

 rrpp a single, rrPp a pea. (Fig. 18). 



1 



Fig 18. — Cross between pea and rose combed 

 fowls: a. pea comb; b, rose comb; c, walunt comb; 

 d, single comb. 



(1) Fi of Single x Rose gives Rose, and Fs gives 3 Rose 

 and 1 Single. 



rp rp = male gametes 



Female ( Rp 

 Gametes -; 



iRp 



Rrpp Rrpp 



Rrpp I Rrpp 



= all Rose 



The diagram of F2 would be : 



Rp rp = male gametes 



Female ( Rp I RRpp | RrpP 



Gametes -| — 



(rp 1 Rrpp 



rrpp 



= 3 Rose and 1 Single 



105 



