THE PROBLEMS IN MATING AND IN EGG PRODUCTION 123 



black, i.e., 3 white to 1 black. It also shows that of the 12 

 whites 4 will be pure, since each gamete is pure (WW), and 8, 

 though white because white is dominant will carry black as a 

 recessive (Wb). By the same table of symbols I find there 

 are 12 rose-combs as R is present in 12 cases, but only 4 pure, 

 where (RR) occurs, and 8 impure (Rs), and that there are 4 

 pure single-combs (ss). 



If I tabulate for rose-combs it appears more simple as — 



RRWW RsWW RsWb ssWW 



RRWb RsWW RsWb ssWb 



RRWb Rsbb RsWb ssWb 



RRbb Rsbb RsWb ssbb 



The tables show me that I get 3 rose-combs to I single- 

 comb, 3 whites to 1 black, and that taking both pairs of charac- 

 ters together there will be out of every 16 chickens, 9 rose- 

 combed whites, 3 rose-combed blacks, 3 single-combed whites, 

 and one singled-combed black. 



A glance at the table will show me the proportion of chickens 

 which will breed true, viz., those which are homozygous for 

 both pairs of characters, e.g., RRWW will breed pure rose- 

 combed whites, and RRbb will breed pure rose-combed blacks, 

 ssWW will breed pure single-combed whites, and ssbb will 

 breed pure single-combed black. 



If the 9 rose-combed whites are taken to breed together, on 

 the average only 1 will breed true, designated above RRWW, 2 

 will throw a proportion of single-combed whites (RsWW). 2 

 will throw also rose-combed blacks (RRWb), while the other 

 4 will throw both single-combed whites and single-combed 

 blacks (RsWb), as well as rose-combs of both colors. 



The awkward part for the breeder is that he is not able, 

 with present knowledge, to tell which will breed true, from 

 outward appearance, but has to test his bi'eeders in these 

 cases by actual experiments, except in the cases above men- 

 tioned, for he knows, e.g., that the single-combed black will 

 breed true. 



These results may be tabulated as below, showing both the 

 outward appearance and the breeding qualities of each chicken, 

 taking the first of the above lists in order — ■ 



