In certain salamanders, the sex of a genetic female can be altered, making her into a functional male; these salamanders are called sex-reversed males. When a sex-reversed male is mated with a normal female, approximately 2/3 of the offspring are female and 1/3 are male. How is sex determined in these salamanders? Explain the results of this cross.

Salamanders determine sex using ZZ/ZW combinations - and in this system, ZZ are male and ZW are female.

 

Now salamanders can reverse sex, and this can be induced by hormones, particularly steroids - no doubt there will be environmental triggers for this.

 

if we have a sex-reversed (ZW) male and a normal (ZW) female, then we have the following combinations for the offspring (just do the punnet square)

 

ZZ, ZW, ZW and WW.

 

I would expect that much like you cannot have a y-y offspring in humans (but you can have XX, XY) because essential genes are missing on the y chromosome, the situation is the same with the ZW combination - WW is simply not viable, so the only offspring that are born are the ZZ (male) ZW and ZW (both female), explaining the 2/3 - 1/3 ratio.