Practice question

Avian sex determination contrasts with mammalian XX-XY system. Birds utilize ZZ-ZW mechanism where males are homogametic ZZ and females heterogametic ZW. Dosage of DMRT1 gene on Z chromosome drives testis development; higher dose in ZZ promotes SOX9 expression, while single dose in ZW allows ovarian fate. W chromosome carries female determining factors like HINTW. Unlike temperature or X0 systems, ZZ-ZW is genetic. This system affects gonadal differentiation, secondary sexual traits and avian breeding strategies. Understanding is crucial for poultry sexing and evolutionary comparison of sex chromosome mechanisms across vertebrates and independent origin of sex determination.