LINKAGE RELATIONS IN MENDELISM 113 
When, therefore, the F; females are mated to yellow white males of 
the genetic constitution (ywX)Y the progeny will give directly in its 
phenotypic ratio the proportions in which the gametes are produced as 
follows: 
49.45 gray white:49.45 yellow red:0.55 gray red:0.55 yellow white. 
The actual experimental results from this type of mating are summarized 
inTable XXII. Theactual linkage value obtained is 1.13 which is substan- 
tially the same as that shown in the previous table. On the basis of sum- 
marized data of counts of 81,299 flies, Morgan and Bridges fix the value 
for crossing-over between these two loci at 1.1 per cent. This is the value 
we have used in deriving the above gametic ratios. Other factors have 
been studied in the same way and give different percentages of crossing- 
over. Thus Morgan and Bridges report the value for crossing-over 
between white and miniature based on counts of 110,701 flies at 33.2 
per cent., between white and vermilion from 27,962 flies at 30.5, between 
vermilion and bar from 23,522 flies at 23.9, and so on for the whole series 
of factors in the first group. 
TaBLe XXII.—Facror Lingkace IN GRAY-RED FEMALE DROSOPHILAS OF THE TYPE 
(YwNX)(yWX) 
Non-cross-overs Cross-overs 
Number |Percentage 
Reported by | of flies | of cross- 
| classified | Gray Yellow Gray Yellow ing-over 
| white | red red white 
Wer tere eee | 1,348 | 440 889 is | 3 1.41 
Morgan and Cattell... .| 3,258 | 1,841 1,412 4 1 0.15 
Morgan and Cattell..... 9,027 | 4,292 4,605 86 44 1.44 
Nn hals anaes | 13,633 | 6,573 | 6,906 | 106 48 113 
Factors in the second and third groups display the same type of 
linkage relations as those in the first group. As an example we may take 
the recessive factors black and curved which lie in the second group. A 
black curved female of the genetic constitution (bc,)(be,) crossed with 
a gray normal male (BC,)(BC,) gives in FP; gray long females and males 
of the genetic constitution (BC,)(be,). When such F, females are 
crossed back to black curved males the results as reported by Sturtevant 
and Bridges are given in Table XXIII. The observed percentage of 
crossing-over between the loci B and C, in the second chromosome in 
this experiment amounts to 24.04 per cent. 
When gray curved females (Bc,)(Be,) are mated to black normal 
males (bC,)(bC,) the F, flies are gray normal as in the previous case, 
but genetically they are of the constitution (Bc,)(bC,). Such females 
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