Summary
Following an outcross to a nonrelated production-bred strain, a White Leghorn stock no longer segregated for diplopodia in the normal 3:1 phenotypic ratio but produced significant deficiencies of diplopod phenotypes. A program of selection over a period of seven years was successful in creating three lines producing significantly different ratios. Line I was restored to the normal 3:1 ratio (26·2% diplopods); line III produced an average incidence ranging from 7·8% to a low of 4·3%; and line II gave intermediate levels ranging from a high value of 17·4% to 8·2% in the last year’s progeny.
The deficiency of diplopods could not be accounted for on the basis of early zygotic mortality and resulting unidentified embryos, or by differential fertility levels in the lines or in individual matings.
Data obtained from crosses between the lines and from backcrosses of linecross progeny could not be explained by the assumption of a simple genetic modifying factor. Occasional evidences for simple dominance or sex-linkage were not verified by more critical tests. A new mutant gene for diplopodia, discovered by Landauer, did not appear to be present in this flock.
A polygenic system of modifying factors derived from the production-bred flock offers the best explanation of the heritable suppression of diplopod phenotypes.
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Taylor, L.W., Abbott, U.K. & Gunns, C.A. Further studies on diplopodia. J Genet 56, 161–178 (1959). https://doi.org/10.1007/BF02984743
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DOI: https://doi.org/10.1007/BF02984743