Multiple gender selection techniques have been tried with spermatozoa. For example, one approach, known as the Ericsson Method, relied on the observation that male sperm are lighter and swim faster, and so they should be able to be separated by weight using spinning. However, this approach has not held up to scientific rigor.Sperm microsorting is a much better technique. It differentiates between male and female sperm based on the amount of DNA that is in the sperm. Sperm carrying a X chromosome has approximately 2.8% more DNA than a sperm carrying a Y chromosome. By using a special dye, the sperm with more DNA material will shine more brightly, and this facilitates microsorting which separates the sperm by sex. It is a proven way to enrich a sperm sample for a gender preference.