In animals, what is the primary role of the Y chromosome?

The primary role of the Y chromosome in animals, particularly in the context of determining male sex characteristics, is foundational in the understanding of sexual differentiation. The Y chromosome carries genes that are essential for the development of male gonads (testes) and the production of male hormones, such as testosterone.

One of the key genes located on the Y chromosome is SRY (sex-determining region Y), which initiates the process of male sex determination during embryonic development. When the SRY gene is expressed, it triggers the formation of testes, which subsequently produce male sex hormones that drive the development of male physical characteristics, including the formation of male reproductive structures and secondary sexual traits.

This biological basis illustrates why the Y chromosome is fundamentally linked to male sex determination and characteristics, reinforcing the importance of this chromosome in the genetic framework of sexual differentiation in animals. Other roles mentioned, such as hormonal balance or influences on body size, do not primarily stem from the specific function of the Y chromosome in regard to sex determination.