In mammals, the presence of the Y chromosome during embryonic development decides whether its offspring will be male or female. Although that is usually the case in mammals, The Amami spiny rat is something extraordinary for they lack Y chromosomes and Sry genes. The Sry gene—Sex-determining Region Y—is located on the short branch of the Y chromosome which initiates the embryonic development of males. In male Amami spiny rats, they only have one X chromosome, while females have both XX.
To understand the gene expression differences in female and male, Cheryl Rosenfeld collaborated with Asato Kuroiwa from Hokkaido University Takamichi Jogahara of the Frontier Science Research Center in Japan, and Scott Givan, associate director of the MU Informatics Research Core Facility to experiment on brain activity of Amami spiny rats. They collected brain samples were collected and RNA was sequenced to compare. Male encoded for various zinc finger protein genes which could be what balanced the loss of SRY genes. The gonad then progressed as testes as a way to help program the brain to be a male. The absence of zinc finger protein led to the development of female. By turning on all the zinc finger proteins this stimulates the differentiation in the sexes.
Animals that are not mammals have different sex-determination than humans. I think people are so focused and interested in learning about the SRY genes that people tend to overlook that there are other contributing factors in the determination of sexes. By researching more on unexplained sexes with the absences of the Y chromosome, we can fully go in depth on how gonadal and brain sexual differentiation works for different animals.