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Females typically have two of the same kind of sex chromosome (XX), and are called the homogametic sex.
Males typically have two different kinds of sex chromosomes (XY), and are called the heterogametic sex.
In mammals, including humans, the SRY gene is responsible with triggering the development of non-differentiated gonads into testes, rather than ovaries.
In the absence of SRY and SOX9, no testes can develop and the path is clear for the development of ovaries.Other less common chromosomal arrangements include: triple X syndrome, 48, XXXX, and 49, XXXXX.In most mammals, sex is determined by presence of the Y chromosome.Exceptions to this are cases of XX males or XY females, or other syndromes.The XY system contrasts in several ways with the ZW sex-determination system found in birds, some insects, many reptiles, and various other animals, in which the heterogametic sex is female.
In these species, one or more genes are present on their Y chromosome that determine maleness.