A review of current concepts on sex determination in animals
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Despite being a complex development process, sex determination is important in reproduction of farm animals. Chromosome sex, which is based on the presence of sex chromosomes, is the most common to scientists. Most common to the layman, is what can be termed phenotypic sex, which is based on what can be seen in an individual. It encompasses the urogenital, external features, such as the external genitalia and secondary sex characteristics. From a molecular genetics point of view, there is also what is termed genetic sex, which is based on the presence of a sex-determining gene. In other words, an XY individual without the sex-determining gene is not a genetic male. The sex-determining gene is located on the Y-chromosome. Since 1959, when the Y-chromosome was shown to be the male-determining factor, there has been controversy as to what really determines sex in animals. However, the identification of what has been termed the sex-determining gene on the Y-chromosome (SRY) in 1990 has narrowed the controversy to the actual mechanism of sex determination. This review focuses on the genetic sex-determination mechanism by which genes determine sex, the fate of the supporting cells and evidence on issues, which are still inconclusive.