Chapter 14 



GENETICS OF FUNGI 



The principles upon which the science of genetics rests were 

 established by Mendel in 1865 but remained unrecognized until 

 the beginning of the present century. He determined from hy- 

 bridization experiments with peas that heritable characters behave 

 as units. These characters may be allelomorphic, that is, they 

 may operate as pairs, one member of which is dominant, the other 

 recessive. The characters must therefore be controlled by factors 

 or determiners which maintain their individuality throughout the 

 developmental cycle and are transmitted from generation to gen- 

 eration. Moreover, in the second hybrid generation or later these 

 characters segregate or become assorted in definite numerical 



ratios. 



With the rediscovery of Mendelism at the beginning of the 

 twentieth century attention turned largely to studies of genetics 

 of seed plants and higher animals. The application of Mendelism 

 to fungi has constituted a neglected field of inquiry until the past 

 few years. Some of the reasons will become apparent in the ac- 

 count that follows. Not the least of them is the small size of nuclei 

 and chromosomes and their constituents. These facts militate 

 seriously against the procurement of microscopic evidence to sub- 

 stantiate macroscopic evidence of inheritance. 



SEXUAL AND ASEXUAL STAGES OF FUNGI 



In order to appreciate and properly evaluate genetic studies of 

 funo-i it is necessary to recall certain knowledge that is funda- 

 mentally axiomatic. In the normal life cycle of fungi generally 

 there occur fusions between pairs of gametes. This phase is 

 called the sexual stage in contrast to the asexual stage, in which 

 vegetative units are capable independently of propagating the 

 fungus. The fusion of gametes, called fertilization, produces a 



317 



