384 HYBRIDS ALLELOMORPHS 



First generation : Td (all tall). 



Second generation: iT: id: 2Td (one tall, one dwarf, two 

 hybrids). 



A considerable number of other pairs of characters have been 

 studied in the same way, with identical results, though there 

 are a number of exceptions, some of which are at present 

 inexplicable. 



The latent character is usually spoken of as the recessive 

 and the other as the dominant. In the experiment with tall 

 and dwarf Peas above described, where the difference is one of 

 size, it is believed by many that the dwarf habit is due rather 

 to the absence of a character causing tallness than to the presence 

 of a special character for dwarfness. And it may well be that 

 in all cases the recessive character is caused by the absence of 

 something which determines the dominant (e.g. a glabrous form 

 of a particular plant may be due to the absence of a character 

 for hairiness, etc.). Pairs of characters, which thus combine in 

 the first hybrid generation and segregate in the subsequent 

 generations, are termed allelomorphs. The following are further 

 examples, the dominant character in each case being that first 

 named. 



Yellow and green, round and wrinkled seeds in Peas. 

 Prickly and smooth fruits (Thornapple, Field Buttercup). 

 Susceptibility and resistance to Rust in Wheat. 

 Starchy and sugary endosperm in Maize. 

 Hard (glutenous) and soft (starchy) endosperm in Wheat. 



A feature which may be of great significance is that almost all 

 the mutants so far studied behave as recessives to the parent 

 stocks from which they sprang. It may be added that recent 

 research has shown that many apparently simple characters can 

 be analysed into a number of subordinate ones, which, however, 

 are very commonly inherited together. 



The most important principle, demonstrated by the experi- 

 ments of Mendel and subsequent workers in this field, is that 

 the characters introduced by either parent do not become 'in- 

 extricably intermingled in the hybrid offspring, but become 

 separated out again in the gametes ; that is to say, each of 



