Genomic mapping and comparative genomics of candidate loci
regions
The candidate loci that we identified were located in intronic regions
of the following genes. The locus 602-G/C is in one of the introns of
the gene FAM135A (DUF676 domain-containing protein), a relatively
unknown domain with GO terms annotation related to cellular metabolic
processes with putative lipase activity and QTLs associated with
regulation of fat intramuscular deposition in chickens and cattle breeds
(Poleti et al., 2018; Yuan et al., 2022). This section of our contig 602
is apparently orthologous to a similar region on the Gallus
gallus chromosome 3, and a region conserved across other bird taxa. The
locus 3657-C/T was found within the gene formimidoyltransferase
cyclodeaminase (FTCD ) and flanked by a feather β-keratin
(BISK1) and collagen alpha-2(chain VI) (ColA62 ) (Fig. 2).
The FTCD is a single copy gene coding for a key component of the
folate metabolism (Wernimont et al., 2011). It also expresses a
bifunctional enzyme involved in starvation-induce responses by
downregulating the mTORC1 pathway towards the maintenance of homeostasis
under low resource conditions (Zhang et al., 2021). While this region is
also in synteny among other bird taxa (with the ColA62 +FTCD clustering in the same orientation), the BISK1 is a
relatively recently discovered copy of a β-keratin identified primarily
in chicken but present also in blue and great tit genomes (Fig. 2). The
novelty falls on BISK1 , a recently identified β-keratin found to
be expressed only in cells defining pennaceous barbules in the contour
feathers of chickens (Kowata et al., 2014).