Steroid isolation , depending on context, is the isolation of chemical matter required for chemical structure elucidation, derivitzation or degradation chemistry, biological testing, and other research needs (generally milligrams to grams, but often more  or the isolation of "analytical quantities" of the substance of interest (where the focus is on identifying and quantifying the substance (for example, in biological tissue or fluid). The amount isolated depends on the analytical method, but is generally less than one microgram.  [ page needed ] The methods of isolation to achieve the two scales of product are distinct, but include extraction , precipitation, adsorption , chromatography , and crystallization . In both cases, the isolated substance is purified to chemical homogeneity; combined separation and analytical methods, such as LC-MS , are chosen to be "orthogonal"—achieving their separations based on distinct modes of interaction between substance and isolating matrix—to detect a single species in the pure sample. Structure determination refers to the methods to determine the chemical structure of an isolated pure steroid, using an evolving array of chemical and physical methods which have included NMR and small-molecule crystallography .  :10–19 Methods of analysis overlap both of the above areas, emphasizing analytical methods to determining if a steroid is present in a mixture and determining its quantity. 
XY individuals carrying duplications of Xp21 undergo sex reversal and develop as females. Swain et al. (1998) noted that XY mice carrying extra copies of Dax1 as a transgene show delayed testis development when the gene is expressed at high levels, but do not normally show sex reversal. Swain et al. (1998) found that complete sex reversal occurred, however, when the transgene was tested against weak alleles of the sex-determining Y-chromosome gene Sry ( 480000 ). These results showed that Dax1 is largely, if not solely, responsible for dosage-sensitive sex reversal and provided a model for early events in mammalian sex determination, when precise levels and timing of gene expression are critical. The results of Swain et al. (1998) indicated that Dax1 functions as an anti-testis gene by acting antagonistically to Sry. The orphan nuclear receptor Dax1 was originally proposed to act as an 'anti-testis' factor. In studies in the mouse, however, Meeks et al. (2003) found that Nr0b1 is in fact required for testis differentiation. Sex reversal in the absence of Dax1 occurred after normal expression of Sry, suggesting that Sry and Dax1 are both required for normal testis determination.