_IMG_21_10bGeneFamilies-L.jpg Multigene families. The oxygen-carrying hemoglobin comprises two kinds of polypeptides coded by families of genes on different chromosomes. Chromosome 16 contains the α-globin gene family. Chromosome 11 contains the β-globin gene family. Each family contains functional _SPAN_NAVY genes as well as nonfunctional _SPAN_GREEN pseudogenes. Humans express different versions of the gene in each family as they develop from embryo to fetus and adult. These genes evolved from _SIZ_duplication.html duplication and mutation of an ancestral globin gene.