Molecular Approaches for Gender Identification and Sperm Sex Ratio Determination in Farm Animals

Mammalian males are heterogametic (XY), while females are homogametic (XX). The accurate identification of the X- and Y-chromosome bearing sperm population and sort them precisely before fertilization event holds promising applications in gender pre-selection and for effectively managing the herds of farm animals.Further, gender identification of embryos during early pregnancy has also been a subject of great interest for animal breeders. Interestingly, the recent reports demonstrated the significant deviation of X- and Y- sperm population from normal (1:1) sperm sex ratio within ejaculates from the same bull or among different bulls. Several techniques, based on the different hypotheses proposed by different research groups, have been used for semen sexing. But none of these, except for flow cytometry based semen sexing, gained wide acceptability due to their low reproducibility and accuracy. Moreover, the reanalysis of flow sorted sperm populations is still required to further validate the purity of the sexed semen. The most commonly used molecular techniques for purity validation of sexed semen include fluorescence in situ hybridization and polymerase chain reaction based approaches. The present review discusses the use of these molecular techniques for gender identification, sperm sex ratio determination and purity validation of semen sexing techniques in farm animals.