In its simplest definition, sex is genetically determined by the X- and Y- chromosomes. It is defined at the time of gonad formation in embryonic development. In humans, the female gamete is referred to as 'X'; the male gamete may be X or Y. Merged at the union, an XX offspring will be female, an XY offspring will be male.
             Testes formation in men is regulated by the expression of genes on the Y chromosome. Ovary formation occurs if the Y chromosome is not present and this DNA is not expressed. Gonads also control the production of hormones like estrogen and testosterone that is key for the development of secondary sex characteristics later in life and these often emphasize the assignment of biological sex.
             At first glance sex identification appears simple. The problem is that sometimes errors occur and offspring may be X0, XXY or XYY. The ability of the genes within the zygote or embryo to produce a male or female individual may be blurred. Errors may occur in the complex process of development. So, it becomes apparent that aneuploidy is a possibility and can make sexual identification complex.
             In addition, gender identity is also an element to consider here. It refers to the psychological self-identification of an individual as female or male. Usually sex and gender identity correspond to each other, but unusual genetics may lead to biological sex ambiguities and gender identity confusion.
             A person's sex can be considered across various levels. Genes, hormones, and genitalia can all be considered physical markers of a person's sex. But behaviors such as gender identity and sexual orientation can be perceived as stereotypically male or female.
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