FIGURE 4. Schematic representation of molecular mechanisms involved in determining the fate of the undifferentiated gonadal ridge. Black arrows indicate a positive regulation; double arrows indicate a positive feedback loop; red lines indicate a negative regulation; double red lines indicate a mutual antagonism. In the 6th week of embryonic life, the gonadal ridge is sexually undifferentiated, and various factors are expressed at the same levels in the XX and the XY gonads. During the 7th week, in the XY gonad, SRY expression is triggered, and the male pathway prevails driving to the formation of the coelomic vessel. In the XX gonad, the female pathway prevails, and there is no formation of the coelomic vessel. Reprinted with permission from ref. (129) Freire AV, Ropelato MG, Rey R. Ovaries and Testes. In: Kovacs C, Deal C, Eds. Maternal-Fetal and Neonatal Endocrinology. 1st Edition. Boston: Academic Press-Elsevier, 2020, pp. 625-641. ISBN 9780128148235. Copyright © 2020 Elsevier Inc.