An elongated segment of DNA observed between two human alpha globin genes.

Detailed restriction enzyme analysis of the DNA from a Chinese female showed that one of her chromosomes had a greater than 17.5 kb deletion of DNA, including the psi alpha, alpha 2, and alpha 1 globin genes, which is present in many Southeast Asians with an alpha-thalassemia-1 chromosome. Her "normal" chromosome had the expected cluster of alpha-like globin genes (5'-zeta-psi zeta-psi alpha-alpha 2-alpha 1-3'), but the segment of DNA between the two alpha globin genes was elongated by some 0.5-0.7 kb. Analyses of various restriction sites suggested that this normal variant of the human alpha globin gene complex is due to a crossover between a normal chromosome with (alpha alpha) and a chromosome with an alpha-thalassemia-2 (-alpha 3.7) and an -alpha 2 alpha 1-hybrid gene.