Is this a male, or a female cat?

This kind of coat coloring, which combines two colors other than white (black and red in this case), is known as tortoiseshell, and it is found almost exclusively in female cats. This is because the X chromosome determines the color of the cat, and there are no color genes in Y chromosome. Thus, female cats with XX chromosomes may be three colored (including white), while male cats with XY chromosomes cannot. (with the exception of very rare XXY sterile males).