Human ?-globin locus
The human β-globin locus is composed of five genes located on a short region of chromosome 11, responsible for the creation of the beta parts (roughly half) of the oxygen transport protein Hemoglobin. Mutant β-globin is responsible for the sickling of red blood cells seen in sickle cell anemia. Expression of all five genes is controlled by single locus control region (LCR), and the genes are differentially expressed throughout development. 
The spatial orientation of the genes comprising the human β-globin locus is essential to their proper regulation. If the genes are rearranged, the gene products are expressed at improper stages of development. The arrangement of the genes directly reflects the temporal differentiation of their expression during development, with the early-embryonic stage version of the gene located closest to the LCR. This indicates that the spatial arrangement and order of the genes with respect to the LCR facilitates their differential expression during development. Thus, the clustering of these genes assists in their tightly regulated developmental expression.
- Levings, P. and Bungert, J. The human β-globin locus control region: A center of attraction. Eur. J. Biochem 2002 Feb; 269:1589-1599.