Аннотация:The current hypothesis suggests that the segregated α- and β-globin gene domains of mammals and birds [1] originated via duplication of an ancestral domain of globin genes, in which the α- and β-globin genes were not segregated [2]. There are good reasons to believe that the ancestral globin gene locus was syntenic to the α-globin gene domains of warm-blooded animals [3]. In this ancestral locus the alpha and beta globin genes are thought to be organized in pairs and transcribed in opposite direction. This organization of globin gene locus still can be observed in modern fish, in particular, in Danio rerio major and minor globin gene loci [3]. In the clusters of α- and β-globin genes of birds and mammals, all globin genes are transcribed in the same direction [1,3]. Although evolution of globin gene loci has been discussed for many years [4], nobody has yet suggested a reasonable explanation for the loss of ancestral organization of α- and β-globin genes into pairs transcribed in opposite directions. This organization appears advantageous as it may allow coordinated expression of α- and β-globin chains that ideally should be produced in equimolar amounts. In a recent publication [5], we suggested that bidirectional transcription of globin genes may be incompatible with the organization of regulatory systems of segregated clusters of α- and β-globin genes in birds and mammals. For example, a unidirectional pervasive transcription of the whole globin gene loci initiated at upstream enhancers [6–10] could interfere with transcrip- tion of globin genes in the opposite direction. To test our hypothesis, here we analyzed whether transcription of a reporter gene inserted into the alpha-globin gene domain in chicken erythroid cells depends on the orientation of the reporter gene.