We need a test that can tell us if there is a function Sr-Y gene or not. That gene is what initiates the cascade of changes that differentiate males and females in humans. There are adult human females with XY genotype but XX phenotype, including a fully functional female reproductive tract and demonstrated capability to produce offspring. The key is that they lack a functional Sr-Y gene and thus the XY genotype is never expressed. Another gene, upstream of Sr-Y, Chromobox homolog 2 (CBX2), can cause a similar break in the sex determination cascade.
The one other edge case I've heard of involve chimeras, individuals with more than one genotype. Most of their cells will be XX but a few will be XY. If those cells are the "right" ones then they can get a pretty substantial boost in physical performance.
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We need a test that can tell us if there is a function Sr-Y gene or not. That gene is what initiates the cascade of changes that differentiate males and females in humans. There are adult human females with XY genotype but XX phenotype, including a fully functional female reproductive tract and demonstrated capability to produce offspring. The key is that they lack a functional Sr-Y gene and thus the XY genotype is never expressed. Another gene, upstream of Sr-Y, Chromobox homolog 2 (CBX2), can cause a similar break in the sex determination cascade.
The one other edge case I've heard of involve chimeras, individuals with more than one genotype. Most of their cells will be XX but a few will be XY. If those cells are the "right" ones then they can get a pretty substantial boost in physical performance.
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