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Abstract

The melanocortin 1-receptor (MCl-R) gene has been associated with E locus phenotypes in chickens. Variant alleles of the E locus are important for accurate down color sexing and also for the inhibition of unwanted tissue pigmentation in broilers. PCR (polymerase chain reaction) based tests for various replacement substitutions found in the published E allele sequences gave unexpected results when tested against known alleles of the E locus. To resolve these issues and gain a better understanding of how replacement substitutions in the MCl-R gene are affecting E locus phenotypes, a number of accessions of the e+, eb, wheaten ( ewh and eY), and the birch in (£R) alleles were PCR cloned and sequenced. The published e+ allele sequence is likely to be a wheaten sequence. All three new wheaten sequences produced an inferred amino add sequence that was identical to the published e+ sequence, but all three of our new e+ sequences had a Thr143Ala polymorphism. All E alleles sequenced except for the new wheaten alleles have Thr143, indicating that the Ala143 mutation may be associated with restriction of black pigment in the feathers. The two recessive eb sequences had the Lys92 mutation associated with extended black in both chickens and mice, but they also had a His215Pro substitution. The Pro215 mutation is a likely candidate to attenuate the Lys92 mutation producing a brown instead of a black female. The Leghorn birchin allele had the Lys91 mutation, but the Fayoumi birchin allele did not. Instead, the Fayoumi sequence had a Leu133Gln substitution.

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