Organization of the chorion genes of Bombyx mori, a multigene family. III. Detailed marker composition of three gene clusters.

The chorion patterns produced by progeny from crosses that were used to define the linked gene clusters, Ch 1, Ch 2 and Ch 3 (strain C108 vs. strain Ascoli), were examined by two-dimensional gel electrophoresis (isoelectric focusing vs. SDS/urea). Approximately 60 proteins were assigned to four previously defined chorion classes, A, B, C and Hc, believed to represent the products of related genes, on the basis of size and relative cysteine content. All strain-specific markers showed co-dominance in the F1, indicating the likelihood that they are not products of post-translational modification. Twenty-seven Ascoli markers co-segregated in testcross progeny, and none of the resolved proteins showed independent assortment, confirming their linkage to chromosome 2. Two-dimensional screening of recombinants demonstrated that all three clusters contain Class A and B markers; Hc markers have been found only in Ch 1 and Ch 2; whereas, mapped C markers were confined to Ch 3. This indicates that chorion clusters are heterogeneous with respect to the markers they contain.