Experimental Analysis of a Paternally Inherited Extrachromosomal Factor

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RESUMO

Virtually all known cases of extrachromosomal inheritance involve cytoplasmic inheritance through the maternal line. Recently, a paternally transmitted factor that causes the production of all-male families has been discovered in a parasitic wasp. The wasp has haplodiploid sex determination: male offspring are haploid and usually develop from unfertilized eggs, whereas females are diploid and usually develop from fertilized eggs. It has been postulated that this paternal sex-ratio factor (psr) is either (1) an infectious agent (a venereal disease) that is transmitted to the female reproductive tract during copulation with an infected male and, subsequently, causes all-male families or (2) a male cytoplasmic factor that is transmitted by sperm to eggs upon egg fertilization and, somehow, causes loss of the paternal set of chromosomes.—Experimental evidence is presented which shows that the factor requires egg fertilization for transmission to the next generation; therefore, it is likely to be a cytoplasmic factor. Significant potential intragenomic conflict results from the presence of this factor and two other sex-ratio distorters in this wasp species.

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