Practice question

Female birds determined genetically by presence of ZW chromosome constitution rather than hormonal milieu. Reduced dosage of Z-linked DMRT1 below biallelic threshold together with W-linked genes HINTW and FET1 triggers ovarian pathway. ZW supporting cells differentiate into granulosa-like cells producing estrogen and oocytes develop asymmetrically with functional left ovary. Cells exhibit cell-autonomous sexual identity evidenced by gynandromorphs. Unlike mammals where Y presence drives male, birds employ female heterogamety whereby ZW genotype directs ovary formation, illustrating independent evolutionary solution for gonadal sex determination.