Disclosed are methods for gender specifically separating a population of sperm cells or non-human embryos. Said methods comprise contacting the population with a labelled locked nucleic acid capable of binding to gender-specific tandem repeat sequences in a portion of the population to provide a labelled fraction and an unlabelled fraction, then separating the labelled from the unlabelled. Also disclosed are sperm cells and non-human embryos comprising a labelled locked nucleic acid bound to a gender-specific repeat sequence
