Male: spelled with­out a Y

The Hamilton Spectator - - HEALTH -

In most mam­mals, us in­cluded, bi­o­log­i­cal sex is de­ter­mined by a lot­tery be­tween two let­ters: X and Y, the sex chro­mo­somes. But there are rare, mys­te­ri­ous ex­cep­tions: A small num­ber of ro­dents have no Y chro­mo­somes, yet are born as fe­males or males, not hermaphrodites. Both fe­male and male Amami spiny rats have only one X chro­mo­some, for ex­am­ple. At some point the rats lost their Y chro­mo­some and, along with it, an im­por­tant gene called SRY that’s con­sid­ered the “mas­ter switch” of male anatom­i­cal de­vel­op­ment in most mam­mals. Re­cently, Ja­panese sci­en­tists in­jected stem cells de­rived from a fe­male rat into male em­bryos of lab­o­ra­tory mice. The cells de­vel­oped into and sur­vived as sperm pre­cur­sors in adult males. This re­sult shows that the spiny rat’s sex cells have “as­tound­ing” flu­id­ity, said Diana Laird, at the Univer­sity of Cal­i­for­nia, San Fran­cisco, who was not part of the study.

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