132 



CHAPTER 10 



Xorl 



centromere 



0.0 0.1 



Hw svr 



S^. \IHnl 



llw 



.SIT 



pn 

 w 

 spl 

 ec 



hi 



rh 

 cv 

 rux 

 cm 



ct 

 sn 



0.8 3.0 6.9 7.5 15.0 18.7 



pn spl bi rb rux cm 



10 unit i of Map Distance 



21 27.7 32.8 38.7 40.7 59.5 



sn Iz ras fw wy fu 



I II I I I 1 1 I I I 



figurh 10—1. Crossover map of the X chromosome of D. melanogaster. 



Name 



yellow body color 



Hairy-wing — extra bristles on wing veins, 

 head, and thorax 



scute — absence of certain bristles, espe- 

 cially scutellars 



silver body color 



prune eye color 



white compound eyes and ocelli 



split bristles 



echinus- — large and rough textured eyes 



bifid — proximal fusion of longitudinal 

 wing veins 



ruby eye color 



crossveinless — crossveins of wings absent 



roughex — eyes small and rough 



carmine eye color 



cut — scalloped wing edges 



singed — bristles and hairs curled and 

 twisted 



Kii ro Symbols 

 Symboi 



OC 



I 



Iz 



ra.s 



v 



m 



fw 



wy 



s 



8 

 sd 



f 

 B 

 fu 



car 

 bb 



Name 



ocelliless — ocelli absent; female sterile 



tan body color 



lozenge — eyes narrow and glossy 



raspberry eye color 



vermilion eye color 



miniature wings 



furrowed eyes 



wavy wings 



sable body color 



garnet eye color 



scalloped wing margins 



forked — bristles curled and twisted 



Bar — narrow eyes 



fused longitudinal wing veins; female 



sterile 

 carnation eye color 

 bobbed — short bristles 



The phenotypic expression of a + allele is 

 usually more viable than that of its mutant 

 forms. For example, in Figure 10-2 the 

 phenotypically split, cut sons are not as 

 viable as the normal (wild-type) sons; al- 

 though both types are equally frequent as 

 zygotes, the former fail to complete their 

 development more often than the latter and, 

 therefore, are relatively less frequent when 

 the adults are scored. Zygotes destined to 

 become either split or cut males are also 

 less viable than zygotes destined to produce 

 wild-type males. Whenever phenotypes are 

 scored after some long developmental pe- 

 riod, much of the error due to differential 

 viability may be avoided by providing op- 

 timal culture conditions. Another way to 

 avoid most of this kind of error is to delay 



the scoring of crossovers for one generation. 

 The cross is arranged in such a way that 

 individuals with the chromosomes to be 

 scored have a homologous chromosome con- 

 taining the normal alleles of all genes under 

 crossover test. Since the progeny of such 

 a cross are phenotypically normal, their 

 viability will be approximately the same, 

 and they can be scored for chromosome 

 type from the offspring each produces when 

 individually test crossed. For example, the 

 female in Figure 10-2 is crossed with wild- 

 type males, and the Fi daughters (all pheno- 

 typically normal) are individually mated to 

 any male. Daughters carrying an X of one 

 of the following types: spl +, + ct, -\ — \-, 

 spl ct — in addition to a H — \- homolog ob- 

 tained from the father — will produce sons of 



