Practice question

Birds display female heterogamety meaning females possess two different sex chromosomes Z and W whereas males possess ZZ. Female produces gametes carrying either Z or W, thus determining sex of offspring analogous to male determination in mammals. Z chromosome is larger and harbors DMRT1 dosage-sensitive testis regulator, while W is small heterochromatic chromosome carrying limited genes including HINTW. Genotype ZW initiates ovarian pathway with asymmetric gonad development, left ovary functional, while ZZ initiates testicular pathway. This contrasting heterogamety highlights independent evolution of sex chromosomes in avian lineage.