Two cysteine substitutions in the MC1R generate the blue variant of the Arctic fox (Alopex lagopus) and prevent expression of the white winter coat.
Level 5 - mechanism / opinion, no new human data
Animal genetic linkage and mechanism study without human clinical data.
PubMed 15982782 · doi:10.1016/j.peptides.2004.11.040
What was done
Researchers sequenced and characterized the melanocortin 1 receptor (MC1R) gene in the blue color variant of the Arctic fox (Alopex lagopus). They performed a family pedigree study in farmed Arctic foxes to test for cosegregation between specific MC1R mutations, the dominant blue coat phenotype, and the suppression of the seasonal white winter coat transition.
What was found
The abstract reports no quantitative sample sizes or statistical values. Two mutations that each insert a novel cysteine residue into the MC1R receptor were identified. The allele carrying both mutations cosegregated completely with dominant expression of the blue coat phenotype and suppressed the normal seasonal change to a white winter coat.
Why it matters
The findings identify specific MC1R receptor alterations underlying the blue coat morph and link the MC1R/agouti regulatory pathway to seasonal coat color molting in mammals.
Limits
The abstract omits sample size, the number of families analyzed, specific functional receptor assay data, and detailed molecular mechanisms explaining how these mutations inhibit seasonal pigmentation changes.
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