Fibromelanosis in Chickens

This test is designed to determine the presence and number of copies of the FM allele associated with dermal hyperpigmentation or Fibromelanosis (FM) in chickens. FM is a unique pigmentation phenotype, primarily seen in the Silkie, Svarthöna, and Ayam Cemani chicken breeds, where it causes extensive black pigmentation of the skin and internal tissues. This pigmentation results from an inverted duplication of genomic regions on Gallus Gallus autosome 20, leading to increased expression of the endothelin 3 (EDN3) gene, a key regulator of melanoblast and melanocyte proliferation. The FM mutation is dominant, so only one copy of the FM allele is needed to express the black phenotype. However, the intensity of pigmentation can vary depending on the number of copies of the allele. Birds with two copies typically exhibit more extensive pigmentation, but expression can vary even in birds with only one copy.

• N/N: No trace of the FM allele was detected
• FM/N: Heterozygous. One copy of the FM allele has been detected
• FM/FM: Homozygous . Two copies of the FM allele have been detected
• IR: Inconclusive results. Although FM allele has been detected we cannot conclude if it a Homozygous (2 copies) or Heterozygous (1 copy). And this is due to the nature of the inverted duplication, where there is a potential for somatic mosaicism to occur as a result of duplication-deletion events. This means that within a single individual, some cells might lose the duplicated region, leading to a mosaic pattern of pigmentation.

This test is particularly useful for breeders aiming to develop pure black lines, as it helps them better understand the relationship between the FM genotype and the resulting phenotypes.