CORROBORATIONS OF MENDEL'S LAW 349 



But let us suppose the impure dominant or dominant-recessive 

 D(R) to be bred with a pure type — e.g. RR (extracted recessive) 

 (in technical phrase, a heterozygote unites with a homozygote). 

 The impure dominant has, by hypothesis, equal numbers of 

 two kinds of germ-cell — let us say, of egg-cell. The pure type 

 has only one kind of germ-cell — let us say, of sperm-cell. The 

 chances of fertilisation should be as follows : 



11 CD + m Qi: egg-cells of impure dominant ; 

 ' « + « 0- ■ sperm-cells of pure recessive : 



The result will be 



n ova Q fertilised by n sperms = n offspring $ 

 n ova © fertilised by n sperms Q = n offspring 



That is to say, equal numbers of impure dominants and pure recessives. 



"This is what actually happens on crossing a fowl having 

 a single comb (RR) with one having a heterozygous ' rose 

 comb.' " 



Or let us suppose the impure dominant D(R) to be bred with 

 a pure dominant DD : 



)j ® -(- ji egg-cells of impure dominant ; 

 n CD + w CD sperm-cells of pure dominant : 

 The result will be n ® + « CD equal numbers of impure dominants and 

 pure dominants. 



" Here again experiment has borne out theory." Therefore, 

 as Mr. Punnett says, " the generalisation known as the principle 

 of gametic segregation may be regarded as firmly established 

 on the phenomena exhibited by plants and animals when strains 

 are crossed which possess pairs of differentiating characters." 



Case of Paired Dominants and Paired Recessives. — A 

 beautiful experiment was made by crossing a variety of pea with 

 Round seeds and Yellow albumen (a pair of dominant characters) 

 with another variety with angular seeds and green albumen (a 

 pair of recessive characters). The result was offspring all like 

 the dominant parent. These hybrids were inbred, and the 

 results were some Round and Yellow, some Round and green, some 



