Pseudogenes - Pseudogene Examples

Pseudogene Examples

The globin gene superfamily provides an interesting example of the generation of both functional and nonfunctional duplicated genes (Figure 3). Based on nucleotide sequence data, it appears that a gene duplication occurred about 600 to 800 million years ago, yielding myoglobin and hemoglobin genes. Another duplication of the hemoglobin gene occurred about 500 million years ago, yielding α-globin and β-globin genes. (Adult human hemoglobin contains two α and two β strands.) These are all functional genes, found on three different human chromosomes. The α-globin and β-globin genes further duplicated, yielding both pseudogenes and functional genes. Possession of more than one globin gene provides a selective advantage because it compensates for the variation of oxygen in the prenatal versus postnatal environment.

The α-globin gene cluster consists of three functional genes and three pseudogenes. There is also an additional gene that is expressed but not incorporated into a hemoglobin molecule. In other words, this would be an example of an expressed pseudogene. The β-globin gene complex consists of five functional genes and one pseudogene. Examples of other processed polypeptide-encoding pseudogenes include those derived from actin, ferritin, and glyceraldehyde 3-phosphate dehydrogenase genes.