Copy number variations of five Y chromosome genes in donkeys

Abstract. In mammals, the Y chromosome plays a pivotal role in male sex determination and is essential for normal sperm production. A number of studies were conducted on Y chromosome genes of various species and identified single-copy and multi-copy genes. However, limited studies about donkey Y chromosome genes have been done. In this study, 263 male samples from 13 Chinese donkey breeds were collected to analyze the copy number variations (CNVs) of five Y chromosome genes using the quantitative PCR (qPCR) method. These five genes (cullin 4 B Y (CUL4BY), equus testis-specific transcript y1 (ETSTY1), equus testis-specific transcript y4 (ETSTY4), equus testis-specific transcript Y 5 (ETSTY5), and sex-determining region Y (SRY) were identified as multi-copy, whose median copy numbers (MCNs) were 5, 45, 2, and 2, and 13 with CNV ranges of 1–57, 1–227, 1–37, 1–86 and 1–152, respectively. The CNVs of these five genes were shared in different breeds. Compared to previous studies, the copy numbers of five genes showed some distinct consequences in this study. In particular, the well-known single-copy SRY gene showed CNVs in donkeys. Our results provided genetic variations of donkey Y chromosome genes.