Sex determination is a fundamental biological process that decides whether an organism develops as male or female. In genetics and evolutionary biology, this process is controlled either by chromosomal mechanisms or by environmental influences. Chromosomal sex determination is based on specific genetic factors carried by sex chromosomes, while environmental sex determination relies on external conditions that affect development. Both systems highlight the evolutionary diversity of reproductive strategies across organisms. In chromosomal sex determination, different organisms employ distinct systems. The XY system, typical of mammals including humans, determines sex based on the presence of the Y chromosome. Males are heterogametic (XY) and females are homogametic (XX). The Y chromosome carries the SRY gene, which initiates male differentiation by promoting testes development. For example, in humans, the absence of a functional SRY gene, even with an XY set, results in female characteristics, showing the gene’s critical role. In contrast, the ZW system is found in birds, some fishes, and reptiles, where females are heterogametic (ZW) and males are homogametic