Is it possible to correctly identify presence of Y chromosome with external physical test only? I asked a question related to the third sex, and I came to know that its always possible to categorize a human to male or female with presence of Y chromosome. Now, I have another question. Is there a way to say if someone has Y chromosome **only with external physical test**? More specifically: * Someone has a penis, can we say that s/he will have Y chromosome? * Some one has Y chromosome, can we say that he will have a penis?

No, an external physical examination would be inconclusive. The reason is the TDF gene. To be more specific, if a person has XY and the gene is not active then the subject would have a female appearance. Also we cannot conclude that a person has a Y chromosome even if it has penis because that gene could be transferred on the X chromosome.

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