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X and Y chromosomes

 
Question:  Why do X and Y chromosomes determine a persons sex?
jbraciak 

Answer:  Human females contain two X chromosomes, and males contain one X and one Y 
chromosome.  In the absence of a Y chromosome, a human fetus will develop as a female.  
This indicates that a gene or genes on the Y chromosome determines "maleness".  Several 
genes that are required for male development have been located on the Y chromosome, but 
as far as I know, the "master" gene has not yet been identified. -Brian

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