Figure 23.9 Some Functional Genes Are Duplicated Many Times as Nonfunctional Pseudogenes (A) The functional gene that encodes ribosomal protein RPL21 is located on human chromosome 13 (indicated in orange). In addition, there are many nonfunctional pseudogenes of RPL21 in the human genome, produced through repeated duplication events (indicated in blue). (B) Although RPL21 represents a relatively extreme example of pseudogene duplication, there are almost as many known pseudogenes in the human genome as there are functional genes.