7f> THE MENDEL JOURNAL 



over chestnut colour, which we call a recessive 

 character. If we sj^mbolise the dominant character by 

 D and the recessive one by R, then each letter will 

 represent a group of sex-cells. A chestnut coloured 

 horse since it carries nothing but chestnut, will, 

 therefore, have only one kind of sex-cell with respect 

 to this character, and its gametic constitution will be 

 represented by R R. Similarly, a pure bay will 

 be represented by D D. But a hybrid or impure 

 bay will contain two classes of sex-cells in equal 

 numbers, namely, those carrying bay and those 

 carrying chestnut. Such an individual will be 

 gametically represented by the symbol D R. 



Now if a pure D D bay stallion be mated with 

 a pure R R chestnut mare, all the foals will be 

 impijre D R bays, because the D sex-cells of the 

 stallion can in reproduction meet nothing but the R 

 sex-cells of the mare. But if an impure D R stallion 

 is mated with an R R chestnut, then the foals will 

 in the long run consist of l)oth bays and chest- 

 nuts in approximately equal numbers. But the 

 bays will be impure or hybrid D R^. In this case 

 the two kinds of sex-cells of the stallion have two 

 possibilities, for its D sex-cells may meet the R 

 sex-cells of the mare, and so also may its R sex-cells. 

 There thus result two unions, a D R or hybrid, and 

 a R R or pure recessive. 



One further feature is of interest. It will be 

 observed that a chestnut horse is one which mani- 

 fests a recessive colour, and must be therefore 

 always pure with regard to this colour ; that is, 



