In some Transformers verisons it's a difference in code, at one point female transformers were created by a scientist (much like Gargamel created Smurfette), in the UK comics Arcee was designed by the Autobots to answer in universe feminist complaints about the lack of women in the team* (no really)...
And then you get the Beast Wars era techno-organic Transformers which was the first time romance became a major portion of western Transformers fiction, and in that generation it seemed like there might be physical differences between the Transformers' gender (especially based on a couple lines by Rat Trap).
There was also an interesting fan concept for a toy line where male and female transformers weapons could combine to form new robots (and hence the weapons are the sex characteristics). The first of several concepts put forward in this video: https://www.youtube.com/watch?v=hGr7wBTxNk8
*I should say that in that case the Transformers were suggested to be a-gender, and so created a Transformer based on their ideas of human femininity, and then were confused when the feminists bashed the new Transformer... On a meta-level it's kind of a mixed bag, the comic is also called Prime's Rib.
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And then you get the Beast Wars era techno-organic Transformers which was the first time romance became a major portion of western Transformers fiction, and in that generation it seemed like there might be physical differences between the Transformers' gender (especially based on a couple lines by Rat Trap).
There was also an interesting fan concept for a toy line where male and female transformers weapons could combine to form new robots (and hence the weapons are the sex characteristics). The first of several concepts put forward in this video: https://www.youtube.com/watch?v=hGr7wBTxNk8
*I should say that in that case the Transformers were suggested to be a-gender, and so created a Transformer based on their ideas of human femininity, and then were confused when the feminists bashed the new Transformer... On a meta-level it's kind of a mixed bag, the comic is also called Prime's Rib.