# Phenotype of White Sika Deer Due to SCF Gene Structural Variation
## 4 Discussion  
Due to the small number of white sika deer, a significant amount of differential information was screened out from the resequencing data as it was not conducive to subsequent analysis. Therefore, we personalized the screened data after AF(allele frequency) analysis by establishing the candidate genome of coat color, which was composed of coat color genes related to a white phenotype and animal albinism in other mammals. We then selectively screened out the required difference regions. However, we only selected the SV and five nonsynonymous mutations located in the exon sequence of the candidate gene, representing the coat color genes that may be related to the white phenotype of sika deer. The exon is an important gene coding sequence in animals, and changes in coat color and related diseases in mammals are mostly caused by mutation of the gene exon region [21]. In addition, synonymous mutation in the exon would not lead to transcription and translation changes, thus not affecting the functional activity of proteins. To summarize, we directly excluded synonymous mutation from the differential information. As the pigment precursor, L-DOPA can be formed into melanin through a subsequent pigment synthesis reaction [24]. The melanosome of melanocytes is the main site of melanin synthesis reactions, which is a membranous organelle [14]. With the accumulation of melanin, melanosome turns black and spreads to surrounding cells [25]. These pigment particles in skin tissue were observed under a microscope. However, there were no pigment particles in the skin tissue of white sika deer, and there was no reaction to L-DOPA, indicating that the pigment synthesis process was completely blocked. However, the white sika deer had black eyes, showing that pigment particles still existed in the eyes, with the pigment synthesis process not being blocked. The sources of melanocytes in mammalian skin and eyes are different. Melancocytes in skin are derived from the neural crest, whereas melanocytes in eyes (melanocyte epithelium) are mainly derived from the neuroectoderm. Although the two melanocytes are differentiated from different cells, both synthesize and store melanin in the cytoplasm [26], and there are no differences in the melanogenesis process. This suggests that the process of pigment synthesis in the skin of white sika is disturbed by other factors. In addition, there are two main ways to synthesize mammalian pigments. The first pathway produces eumelanin, while the second produces brownish melanin [27]. The research showed that the mutations of _TYRP1_, _LYST_[28], _ICAT_, _WRN_, and _EPG5_[29] would lead to hypopigmentation in the skin, coat, and eyes. Although the amount of pigment synthesis in melanocytes is reduced, the synthesis process is not completely blocked. The mutation of a single gene only affects one pathway of pigment synthesis, with no obvious effect on the other pathway. This may be the reason why another clinical manifestation of albinism involved skin, hair, and eye pigment dilution rather than complete albinism, except for albinism caused by _TYR_ gene mutation. The _SCF_ gene not only regulates pigment synthesis, but also participates in the development and migration  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Phenotype** & **Genotype** & **Individuals** & **Amount** \\ \hline White & SCF\({}^{\text{\text{\text{\text{\text{\text{\text  
of melanocytes. The structural variation in the SCF gene had a strong correlation with the coat color changes of white sika deer. In the process of designing primers, we found that the mutation position of the sika deer _SCF_ gene included exons 7, 8, and 9.