608 



MESSRS. J. LEWIS BOXIIOTE AND F. W. SMALLEY OX 



till eventually some birds will be pi'oduced showing only one or 

 two coloured feathers. This matter, however, we shall not 

 discuss at present. 



For our present purpose we may ignore the White character, 

 a.ssuming that it is always present and inherited in common with 

 the Grizzle. The gametic formula, therefore, of a grizzled bird 

 will be BJ3cc or cd GG or Gg, where B is the Blue colour, 

 c &■ d concentrntiion or dilution (the combination dd producing 

 a bird known as a Silver Grizzle), and G & g the presence or 

 absence of Grizzle. Therefore from the crossing of two Grizzles 

 we may either get all Grizzles or Blues and Grizzles, according to 

 whether the birds are homozygous or heterozygous to the Grizzle 

 character. Under the term Blue we here for simplicity's sake 

 include Silver. 



Again, as in the case of the Chequers, the results from pedigrees 

 a.re apt to be misleading owing to the difficulty of distinguishing 

 the homozygous from the heterozygous birds ; nevei'theless such 

 results entirely bear out our hypothesis, since, as regards the 

 colours produced, the results are quite in accordance with ex- 

 pectations. 



Grizzle to Grizzle^'. 



* As befoi'e, only the character dealt with is shown in the Gametic Formula. 



Looking through these matings, we see thafc when both Grizzles 

 and Blues sl^ould have appeared the expected proportion ought to 

 have been 3:1, and the results give 10:5 or a rather large 

 excess of Blues. 



Grizzle to Blue. 



These matings (Exps. 83-138, 152-155) may be divided into two 

 groups : (1) those in which the gametic formulje of both parents 

 were known ; (2) those in wliich, owing to the gametic formula 

 of one parent being doubtful, two expectations were possible. 



Cei'tain of the Grizzles were known to be heterozygous : this was 

 the case in 19 matings, in which therefore Grizzles and Blues 

 should have appeared in approximately equal numbers. Alto- 

 gether 64 young were reared, 37 Grizzles and 27 Blues, thus 

 showino- n slight excess of Grizzles. 



