Multiple Alleles at the a Locus of Maize 279 



The allelic relationship can be proved by a series of crosses. 

 A cross between a chinchilla {c^^c''^) and a Himalayan (c^c^) 

 gives chinchilla (c^^c^) ; but if these types were produced by 

 nonallelic recessive genes on different chromosomes, a cross 

 between them would produce only wild-type offspring. 



Since each gene is completely dominant over those below it 

 in the series, several of these types may be heterozygous. Thus, 

 the wild-type animal may be CC, Cc^^, Cc^, or Cc, the chinchilla 

 may be c^^c^^, c'^'^'c", or c^^c; the Himalayan may be c^c" or 

 c^c; but the albino can be only cc. Keeler and Cobb have 

 shown that a similar series of alleles is also present in cats except 

 that the albino member either does not exist or has not yet been 

 discovered. The chinchilla type is know^n as ^'silver" and the 

 "Himalayan as "Siamese'' in cats, but apparently silver and 

 Siamese stand in exactly the same allelic relationship as do 

 chinchilla and Himalayan in these other mammals (Fig. 82). 



Multiple Alleles at the a Locus of Maize 



In the last two chapters we have mentioned the a locus of 

 maize in connection with the effect of Dt in making the stable 

 gene, a, unstable and in causing it to mutate frequently to A. 

 Emerson and Anderson and Rhoades have discovered eight al- 

 leles at this locus which show a very interesting relationship. 

 These alleles wdth their phenotypic effects are listed in Table 

 10. All these genes produce striking effects on three parts of 

 the plant — ^the aleurone layer, the leaves and stems, and the 

 pericarp. An interesting feature of this series is that one gene 

 may be dominant over another with respect to one part of the 

 plant but recessive to the other gene or may produce the same 

 effect as produced by the other gene in another part of the 

 plant. We find, for example, that a^ is dominant over A in peri- 

 carp color but is recessive to A in aleurone and general plant 

 color. Also, A^ is dominant over A in pericarp color, but has 

 the same effect as A on the color of the aleurone layer and of 

 the stems and leaves. 



