Inheritance and linkage of isozymes in Yponomeuta padellus (Lepidoptera, Yponomeutidae)

Abstract

Inheritance and genetic linkage of 29 allozyme loci were studied by single-pair crosses of Yponomeuta padellus (Lepidoptera, Yponomeutidae). All loci segregated as Mendelian genes with codominant alleles except for a null allele at the hbdh locus. The three loci est-2, 6pgdh, and fudh were sex-linked and occurred in that order along the Z chromosome. Autosomal linkage analysis was facilitated by the lack of crossing-over in females characteristic of Lepidoptera, because linkage in female-informative crosses is all-or-none and observation of 'forbidden recombinants' provides conclusive evidence that two loci are not syntenic. Convincing evidence was found for linkage of the autosomal loci me and mpi. This linkage group and aat-1, Ca, hbdh, hk-1, pgi and pgm were assigned to seven separate autosomes. Weaker evidence from male-informative families supported four additional linked pairs. Previous cytological studies have shown that the sex chromosomes in heterogametic females are associated in a trivalent, consisting of a W chromosome translocated to an autosome (Av), paired with the Z chromosome and the homologous autosome A. Any locus located on this autosome and its homologous segment on the A" chromosome should show strict segregation of one allele to Sons and the other to daughters. However, none of the female-informative loci in this study satisfied that criterion. Use of the method of forbidden recombinants and its utility in the study of chromosomal evolution in Yponomeuta are discussed.

Getting a Full Dose? Reconsidering Sex Chromosome Dosage Compensation in the Silkworm, Bombyx mori

“…Because discerning the sex of the sampled individual would make these data more meaningful in the context of dosage compensation, we assayed SNPs in the data, assuming that only a male would show heterozygosity on the Z. This is a reasonable assumption given that there is ample allozyme evidence for diploid, heterozygous expression of Z-linked loci in male Lepidoptera ( Mallet et al 1993 ; Raijmann et al 1997 ); there is also little evidence for any Z-W homology in Bombyx so it is unlikely that apparent Z-linked heterozygosity could arise from pseudoautosomal regions such as occurs between X and Y chromosomes in humans ( Fujii and Shimada 2007 ). We identified 182 heterozygous Z-linked SNPs, a count which falls squarely in the range detected among autosomes using the same criteria (132–569 SNPs per chromosome).…”

Inheritance and plasticity of adult host acceptance in Yponomeuta species: implications for host shifts in specialist herbivores

“…The accumulation of gene complexes on the Z chromosome could facilitate host shifts, because in the heterogametic sex co-adaption of multiple host use, loci would not be disrupted by recombination (Hagen & Scriber, 1995). However, it is unclear why this phenomenon should be especially pronounced in Lepidoptera (Pashley-Prowell, 1998), since in this insect order female autosomes do not undergo recombination either (Traut & Marec, 1996;Raijmann et al, 1997), and linkage groups will therefore be favoured equally on autosomes and sex chromosomes. Charlesworth et al (1987) showed that the rate of evolution of favourable autosomal mutations exceeds that of X-linked loci if they are semi-dominant or dominant, especially if selection acts on the heterogametic sex.…”

Sex-Linked Hybrid Sterility in a Butterfly

“…There is tentative evidence that lepidopteran Z chromosomes do diverge faster than the autosomes, as many species-diagnostic traits are Z linked, including 24% of differentiated allozyme loci across 11 species comparisons (Sperling 1994;Prowell 1998). However, in Lepidoptera, which generally have chromosome numbers around 30, between 10% and 25% of all polymorphic allozyme loci are Z linked (Mallet et al 1993;Raijmann et al 1997;D. Heckel, pers.…”