An Introduction to a Biology 



or (0*5) of the total heritage of the offspring ; the four 

 grandparents, one quarter, or (0-5)2 . ^j^^ eight great- 

 grandparents, one eighth, or (0-5)3, ^t^^^ gQ qjj^ Thus the 

 sum of the ancestral contributions is expressed by the 

 series {(0-5) + (0*5)2 _|_ (0-5)^, &;c.}, which, being equal to 1, 

 accounts for the whole heritage." (Gal ton, '97, p. 402.) 



(3) Mendel's Investigations 



Mendel, an account of whose life and a translation of 

 whose work has been given by Bateson (:02a), conducted 

 hybridisation experiments with peas in the cloister garden 

 of the monastery at Briinn of which he was Abbot. He 

 had found that peas differed from one another in respect of 

 seven characters, only one of which, for the sake of sim- 

 plicity, I propose to consider ; that is, the colour of the 

 seed : this was either yellow or green. When he crossed a 

 green-seeded pea with a yellow-seeded pea, the hybrid which 

 he obtained was always the same with regard to that char- 

 acter ; it was always a yellow-seeded pea. Yellow-seeded- 

 ness therefore was called a dominant character ; and green- 

 ness of seed a recessive character. When the hybrids were 

 allowed to breed (they were self -fertilised), a curious result 

 was obtained : 25% of the offspring were green-seeded and 

 75% yellow-seeded. Now it will be remembered that the 

 hybrid was yellow-seeded ; and also that that was the 

 character of one of the parents of the hybrid ; so that by 

 mere inspection of the yellow-seededness of this 75%, wo 

 cannot tell whether they are all pure 3^ellows, or all hybrids, 

 or some pure yellows and some hybrids. But we can tell 

 this by breeding from these yellow-seeded peas ; for it is 

 known that pure yellows breed true, and we have just seen 

 that hybrids produce 25% green-seeded and 75% yellow- 

 seeded peas. Suppose we take actually 75 yellow-seeded 

 peas (the number, of course, does not matter, so long as it 

 is large ; but 75 is convenient, as we shall shortly see), and 

 plant some seeds from each plant. What Mendel found 

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