| Popis: |
Institute) have identified four XX males lacking ZFY, but who, never- theless, do possess Y-specific sequences originating from a region of up to 60 kb that abuts the pseudoautosomai boundary 6. These observations clearly indicate that an X/Y exchange must have occurred and suggest strongly that this re- arrangement is a significant factor in the manifestation of sex reversal in these individuals. The focus of the search for TDF has therefore been shifted to the region between the pseudoautosomal boundary and ZFE. What then of the information provided by the XY female whose rearranged Y and 22 chromosomes were deleted for 140 kb including ZFY but, from the original charac- terization, were presumed to have all other regions represented.7 Clearly one could speculate that, although TDF is present, its ex- pression could have been altered as a result of the rearrangement. Fortunately for the clarity of the new position, it turns out that the translocation appears to have resulted in an additional deletion of a region of about 45 kb below the pseudoautosomal boundary (unpublished obser- vations from Page's laboratory, communicated at the meeting). It can be imagined that several groups are now intently searching for an evolutionarily conserved open reading frame in the new critical zone and many look for- ward to an announcement in the near future. Burgoyne 't has argued cogently that testis determination in humans is controlled by a gene, such as that which may now be predicted to exist in the region immediately adjacent to the pseudoautosomal boundary, working in combination with ZFE. Clearly, the details of the differences between humans and mice and between them and the marsupials, where the autosomal location of the presumptive equiv- alents of both ZFX and ZFY sug- gests double doses for both sets of products, provide a stimulating area for further speculation and experimentation. Perhaps all is not lost for the teaching paradigm. The approach of gene mapping may even be rehabilitated - enhanced by its association with the maxim 'if at first you don't succeed, try again'. |
