A very extensive series of observations has been made on the character called abnormal abdomen. There are three loci involved in this cross, namely, cherry, lemon, and vermilion. This order is confirmed by the result that the number of cross-overs between fused and vermilion is greater than that between bar and vermilion.
This is the furthest point yet obtained to the right.
The data are consistent with the assumption that the lemon locus is between cherry and vermilion, for the double cross-over classes the smallest classes are cherry lemon vermilion and wild type. If the gen is sex-linked the non-appearance of dot in the F 1 males can be explained on the ground that males that are genetically dot show dot very rarely, or that its appearance is dependent upon the intensification by an autosomal factor of the effect produced by the sex-linked factor for dot.
Drosophila sex linked traits in Traralgon-Morwell shows that the mother of the original high sex-ratio was heterozygous for a recessive sex-linked lethal. Here, over a hundred characters that have been investigated as to their linkage relations are found to fall into four groups, the members of each group being linked, in the sense that they tend to be transmitted to the gametes in the same combinations in which they entered from the parents.
For three pairs of gens there are eight classes, and in order that each of them may appear as a non-cross-over, as each single cross-over, and as the drosophila sex linked traits in Traralgon-Morwell cross-over, four experiments must be made. Red eye color is wild-type and is dominant to white eye color.
The result indicated that the new black color, which we call sable, was due to a sex-linked factor.
Since the sex-linked gen bow entered from the female, half the F 2 males and females are bow. These three males had also vermilion eyes, indicating linkage of dot and vermilion. Further details of these last two experiments may now be given. There were males, of which 42 were cross-overs between sable drosophila sex linked traits in Traralgon-Morwell rudimentary and 4 between rudimentary and forked.
Rarely the female lays a few eggs; when she does so some of the eggs hatch, and if she has been mated to a rudimentary male, the offspring are rudimentary females and males. The F 2 generation drosophila sex linked traits in Traralgon-Morwell given in table The recessive sex-linked mutation eosin eye-color appeared in August in a culture of white-eyed flies Morgan a.
Ordinarily all the sons and none of the daughters show the recessive sex-linked characters of the mother when the father carries the dominant allelomorph. There is no way from Mendelian data by which this difference between a true case of multiple allelomorphs and one of complete linkage as just illustrated can be determined.
Since the two lethals were in different X chromosomes, all the daughters should receive one or the other lethal, except in those few cases in which crossing over had taken place. The bar daughters were back-crossed to forked fused males and gave the results shown in table Yellow was found to be at the end of the X chromosome, and this end was arbitrarily chosen as the zero or the "left end," while the other gens are spoken of as lying at various distances to the right of yellow.