Sex Determination:
Humans possess 46 chromosomes, split up into 23 pairs. 22 of these pairs are the same in both men and women. These are referred to as autosomal chromosomes and are not involved in sex determination, but determine other important characteristics such as academic ability, eye colour and face shape. The 23rd chromosome however, determines sex, and thus differs in men and women. In women, this chromosome is a matched pair - it is XX. In males however, the 23rd chromosome is unmatched - it is XY. Thus, the presence of the Y chromosome in humans determines their sex; it does not matter how many X chromosome one possesses, as soon as a Y chromosome is added, the person will begin to exhibit masculine characteristics and traits.
As both men and women contain at least one X chromosome, it can be inferred that female gametes (eggs), always contain an X chromosome. Sperm on the other hand, can contain either a Y chromosome or an X chromosome, thus, sex is determined by the chromosomal component of the father's sperm: if an X sperm combined with an egg, the result would be a girl (XX), and the organism will begin to develop ovaries. If however, a Y sperm combined with an egg, the result would be a boy (XY), and the individual will form testes. Therefore the testis determining factor is carried on the Y chromosome - something on this chromosome causes the gonads to develop into testes rather than ovaries.
As both men and women contain at least one X chromosome, it can be inferred that female gametes (eggs), always contain an X chromosome. Sperm on the other hand, can contain either a Y chromosome or an X chromosome, thus, sex is determined by the chromosomal component of the father's sperm: if an X sperm combined with an egg, the result would be a girl (XX), and the organism will begin to develop ovaries. If however, a Y sperm combined with an egg, the result would be a boy (XY), and the individual will form testes. Therefore the testis determining factor is carried on the Y chromosome - something on this chromosome causes the gonads to develop into testes rather than ovaries.