Animal Molecular Breeding 2024, Vol.14, No.2, 165-177 http://animalscipublisher.com/index.php/amb 171 5.2 Results and Interpretation The genetic analysis of the Chinese Rex rabbit population involved genome-wide association studies (GWAS) and sequencing of candidate genes known to influence coat color. Blood samples were collected from 250 Chinese Rex rabbits with six different coat colors, and genome sequencing was performed using a restriction site-associated DNA sequencing approach. A total of 91 546 single nucleotide polymorphisms (SNPs) were identified, distributed across 21 autosomes (Zhang et al., 2023). The GWAS identified 24 significant SNPs located within a genomic region on chromosome 4 (OCU4), with the most significant SNP being OCU4:13 434 448 (p=1.31e-12). This region was found to be significantly associated with coat color in Chinese Rex rabbits, and the well-studied agouti signaling protein (ASIP) gene was located within this region (Figure 2) (Zhang et al., 2023). The ASIP gene is known to play a crucial role in determining coat color by regulating the distribution of eumelanin and pheomelanin pigments. After testing all SNP effects with a mixed linear model (top panel), the most significant SNP (OCU4:13,434,448, p=1.31e-12) was fitted as a covariate for re-testing of SNP effects (middle panel). Both significant SNPs (OCU4:13 434 448, p=1.31e-12 and OCU4:11 344 946, p=7.03e-07) were simultaneously fitted as covariates for re-testing of SNP effects (bottom panel). The dashed line represents the genome-wide significance threshold (Adopted from Zhang et al., 2023) In addition to the ASIP gene, variations in other pigmentation genes such as MC1R, MITF, TYR, TYRP1, and MLPH were also analyzed. For instance, the MC1R gene was found to have multiple alleles associated with different coat colors, including a 30-nucleotide in-frame deletion (c.304_333del30) associated with red/fawn/yellow coat colors and a 6-nucleotide in-frame deletion (c.280_285del6) associated with black coat colors (Fontanesi et al., 2006; Fontanesi et al., 2010; Xiao et al., 2019). Similarly, the TYR gene, which is responsible for albinism, exhibited several missense mutations associated with different coat color phenotypes, such as the albino, Himalayan, and chinchilla alleles (Utzeri et al., 2021). Furthermore, the MLPHgene, which affects coat color dilution, was found to have two variants associated with the dilution phenotype: the c.111-5C>A variant and the c.585delG variant. The c.585delG variant showed a perfect association with the dilution phenotype, and a significant decrease in MLPH transcript levels was observed in rabbits with diluted coat colors. 5.3 Implications for Breeding Programs The findings from this genetic analysis have significant implications for breeding programs aimed at improving coat color traits in domestic rabbits. The identification of specific genetic variants associated with coat color provides valuable molecular markers that can be used in selective breeding programs to achieve desired coat colors. For instance, the identification of the ASIP gene as a major determinant of coat color variation in Chinese Rex rabbits allows breeders to select for specific alleles to produce rabbits with preferred coat colors. Similarly, the variations in the MC1R and TYR genes can be used to predict and select for specific coat color phenotypes, such as red/fawn/yellow or albino rabbits (Fontanesi et al., 2006; Fontanesi et al., 2010; Yang et al., 2015; Xiao et al., 2019; Utzeri et al., 2021). Moreover, the association of the MLPH gene with coat color dilution provides a genetic basis for selecting rabbits with diluted coat colors, which are often preferred in the rabbit fur industry. By selecting for the c.585delG variant, breeders can produce rabbits with consistent and desirable coat color dilution. 6 Applications of Coat Color Genetics in Rabbit Breeding 6.1 Selection for desirable traits in breeding The genetic analysis of coat color variations in domestic rabbits has significant implications for the selection of desirable traits in breeding programs. Coat color is not only an aesthetic trait but also an economic one, influencing the market value of rabbits. The identification of specific genes and their polymorphisms associated with coat color can provide breeders with molecular markers to select for preferred traits more efficiently.
RkJQdWJsaXNoZXIy MjQ4ODYzNA==