GENIC INTERACTION 169 



There are at least two pairs of modifiers, Mp x , mpy, Mp 2 , mp 2 , that profoundly 

 affect the intensity of pale sepias (EBppF), pale browns (EbbppF), and probably the 

 trace of eumelanin in pale brownish creams (Eppff) but have no recognizable effect 

 in dark sepias {EBP), dark browns (EbbP), or yellows (V<?). 1439 There are, however, 

 unanalyzed modifiers that affect the height of the ceiling for black or brown []> (Leu)] 

 as well as those already referred to that affect the ceiling for yellow [T (Lph)]. 



ENVIRONMENTAL EFFECTS ON COAT COLOR 



There are interaction effects with temperature and age 1401, 1421 (figure 25). 

 Most of the processes become weaker as the animals grow older, independently of 

 temperature. Thus pale sepias fall off some 50 to 60 per cent in intensity by a half 

 year of age (attributable to process 22 in figure 22). In dark browns that are not dingy 

 there is a reduction of about 12 per cent, probably from lowering of the ceiling (27 in 

 figure 22). However, the dingy females darken, indicating a weakening of dingy 

 modifiers (28 in figure 22), but the males become even lighter. Experimental evidence 

 indicated that this lightening was an effect of androgens. 1400 Pale browns diminish 

 in intensity but probably somewhat less than pale sepias. Intense yellows (FF) 

 decrease some 20-30 per cent (14 in figure 22), while fading yellows (ff) show a much 

 greater reduction, some 50-60 per cent (15 in figure 22). 



Low temperature has already been referred to as a condition for sootiness of 

 yellow (10 in figure 22). The most striking effects of temperature, however, are 

 those on the lower c alleles, the products of which seem to be markedly thermolabile 

 (12 in figure 22). This effect is not recognizable in the case of C, the product of which 

 is presumably present in great excess. In the case of c k product, the effect of tempera- 

 ture, if any, does not compensate for the reduction with ageing. Thus yellows of 

 genotypes c k c k F, c k c r F, and c k c a F become significantly paler after birth when production 

 of pigment occurs at a lower temperature than before birth. This is also true of sepias 

 carrying c k P. On the other hand, yellows carrying c d F all become more intense. In 

 these, the decreased loss of c d product with lower temperature more than compensates 

 for the effect of ageing. This is also true of dark sepias with c d c d , c d c r , c r c r and especially 

 c d c a and c r c a . Albinos (c a c a ) are pure white at birth, although pigment cells are 

 present. 1204 Soon after birth, those with EBc a c a P and Ebbc a c a P develop much black 

 or brown pigment, respectively, in the skin and in hairs on feet, nose, and ears and 

 traces of eumelanin on the back. In dark browns, the lowering of the ceiling with age 

 and the tendency to darkening, especially of c r c a and c d c a , from lowered temperature 

 almost remove all differences among c compounds except for c a c a and CPPFF males. 



SPOTTING 



We have not yet considered spotting and its remarkable interaction 

 effects. 199, 1439> 1454 Spotting (colored spots on a white ground) depends primarily 



