In birds, males have two Z chromosomes (ZZ) and are homogametic, while females have one Z and one W chromosome (ZW) and are heterogametic. The most likely regulatory mechanism to address potential imbalance in gene expression between male and female birds is inactivation of one Z chromosome in males. This helps equalize expression from the Z chromosome between males and females.

1. In the ZW sex-determination system for birds, males (ZZ) are the homogametic sex while females
(ZW) are the heterogametic sex. What is the most likely regulatory mechanism for the potential
imbalance in gene expression between male and female birds? Post-transcriptional modification of
half the male sex chromosomes gene products Inactivation of one Z chromosome in males Post-
transcriptional modification of half the female sex chromosomes gene products Inactivation of the
W chromosome in females Destruction of one Z chromosome in males