A method of isolating X-chromosome bearing sperm cells and Y-chromosome bearing sperm cells wherein the X-chromosome bearing sperm cells and the Y-chromosome bearing sperm cells have differing sperm cell head volumes, the method comprising the step of providing a fluid stream which contains sperm cells and the steps of: a. generating a beam of electromagnetic radiation having initial waveform characteristics; b. splitting the beam to induce a split larger than the size of the sperm cell head; c. providing polarization adjustment elements allowing a polarization angle to be chosen independently for each split beam; d. traversing said volume of said sperm cell head in the fluid stream with said split beams, thus giving rise to two individual images, separated laterally, originating from one sperm cell head, wherein the initial waveform characteristics are altered by traversing said volume of said sperm cell head; e. detecting independently signals resulting from these two images wherein the polarization angles of the split beams have been chosen in step c so that the signal of one image corresponds to the sperm cell head volume, and the signal of the other image depends upon orientation of the sperm cell head in the fluid stream; f. assessing a volume of the sperm cell head containing the nuclear DNA of said sperm cells by the signal corresponding to the sperm cell head volume; g. assessing the orientation of the sperm cell head using the signal depending upon the orientation of the sperm cell head in the fluid; h. discarding the sperm cell heads not orientated properly to allow a accurate measurement of the sperm cell head volume and differentiating between said X-chromosome bearing sperm cells and said Y-chromosome bearing sperm cells based upon said volume of said sperm cell head containing said nuclear DNA of said sperm cells. a. generating a beam of electromagnetic radiation having initial waveform characteristics; b. splitting the beam to induce a split larger than the size of the sperm cell head; c. providing polarization adjustment elements allowing a polarization angle to be chosen independently for each split beam; d. traversing said volume of said sperm cell head in the fluid stream with said split beams, thus giving rise to two individual images, separated laterally, originating from one sperm cell head, wherein the initial waveform characteristics are altered by traversing said volume of said sperm cell head; e. detecting independently signals resulting from these two images wherein the polarization angles of the split beams have been chosen in step c so that the signal of one image corresponds to the sperm cell head volume, and the signal of the other image depends upon orientation of the sperm cell head in the fluid stream; f. assessing a volume of the sperm cell head containing the nuclear DNA of said sperm cells by the signal corresponding to the sperm cell head volume; g. assessing the orientation of the sperm cell head using the signal depending upon the orientation of the sperm cell head in the fluid; h. discarding the sperm cell heads not orientated properly to allow a accurate measurement of the sperm cell head volume and differentiating between said X-chromosome bearing sperm cells and said Y-chromosome bearing sperm cells based upon said volume of said sperm cell head containing said nuclear DNA of said sperm cells.