An Overview of Sex Selection at Conception in Mammals

Although the mechanisms under which sex ratio is controlled in nature remain unknown, researchers have attempted to treat sperm in an effort to predetermine the sex of the offspring. The methods of sperm separa-tion that have been repeatedly reported to isolate fractions rich in X- or Y-chromosome bearing sperm are serum albumin gradient swim-up and flow cytometry. However, the ability of the serum albumin gradient method to isolate Y-chromosome rich fractions and alter the sex ratio of offspring is still a subject of con-troversy. The flow cytometry technology used to separate X- and Y-bearing sperm into live fractions has been improved and publications showed that the procedure for the capacitation of flow cytometry sorted sperm might be successfully applied for fresh sperm in in vitro fertilisation (IVP) programs. In the case of sexing embryos the use of the polymerase chain reaction (PCR) is a service offered by several embryo transfer practitioners, but it is labor intensive and costly. In addition, biopsied embryos do not survive freez-ing very well. In the near future, PCR assays for use in the predetermination of the sex of offspring may become available. In combination with in vitro maturation (IVM), in vitro fertilisation (IVP) and embryo transfer techniques, it is very likely that sexed spermatozoa or embryo will be used widely and efficiently in mammals where higher numbers of spermatozoa or embryo are usually required. To be commercially vi-able, a method of embryo sexing must be highly efficient, simple and cheap. Although many livestock breeders request embryo sexing, it has not found widespread use especially in developing countries.