MITOCHONDRIAL D-LOOP VARIANTS AS GENETIC MARKERS FOR DISTINGUISHING MORPHOLOGICAL GROUPS IN COMMON CARP CYPRINUS CARPIO

In the rivers of Iraq, two morphologically distinct groups of common carp, Cyprinus carpio, have emerged without human intervention, exhibiting remarkable differences across a wide range of characteristics. Given the significance of the mitochondrial D-loop in regulating mitochondrial functions and subsequent species evolution, this study aimed to investigate whether D-loop variations could serve as genetic markers to distinguish between these two groups, designated as Group I and Group II. Mitochondrial variations were analyzed in 70 samples using Sanger sequencing of D-loop PCR fragments, followed by the construction of a median-joining network and neighbour-joining tree. The morphological differences between the two groups were corroborated by genetic variation, with 17 variants detected, including 3 exclusive to Group I and 2 to Group II. Linkage disequilibrium (LD) analysis showed that these variants were entirely co-inherited within each group. This distribution, combined with network and phylogenetic analyses, revealed that the variations formed two distinct phylogenetic groups with clearly differentiated ancestral origins. Group I exhibited higher mitochondrial diversity and broader haplotyping capacity, suggesting greater biological adaptability. The distinct maternal lineage distributions further support a genetic basis for the observed phenotypic differences. These findings underscore the role of the mitochondrial D-loop in shaping the adaptation of C. carpio to diverse ecological conditions.