Y chromosome
The Y chromosome is a sex chromosome that when present in most animal means the animal would be classified as male. Males have one X chromosome and one Y chromosome (heterogametic); whereas females have two X chromosomes (homogametic). The Y chromosome is also much smaller then that of the X chromosome, and therefore contains less genes, leading to X-linked disorders. Although in moths, butterflies, some fish and most birds it is the female that is heterogametic. So there is no confusion when writing about these genetic differences, the nomenclature of ZZ/ZW (instead of XX/XY) [1].
Features
The pseudoautosomal region (PARS) is the region of the Y chromosome that is homologous with the X chromosome. During meiosis, theses two homologous regions synapse and recombine.
The male specific region of the Y (MSY) is not homologous with the X chromosome, and therefore is unable to synapse with the X chromosome.
The sex determining region of Y produces testis determining factor (TDF). TDF is what causes testes to form from undifferentiated gonadal tissue when an embryo is developing.