What are pseudogenes?What is their purpose?

Answer 1

Pseudogenes look like normal genes but do not express any RNA or protein. They include supposedly crippled copies of known functional genes, LINEs (long interspersed repeats) and SINEs (short interspersed repeats). It has been shown how testable and repeatable science is displacing the evolutionary concept that pseudogenes are nonfunctional and that they can be used in establishing primate phylogenies. Some highlights are presented here.

Pseudogenes are often referred to in the scientific literature as nonfunctional DNA, and are regarded as junk. But more scientists are now conceding that this is far from true for many pseudogenes. Failure to observe pseudogenes coding for a product under experimental conditions is no proof that they never do so inside an organism. It is also impossible to rule out protein expression based solely on sequence information, as DNA messages can be altered by, e.g. editing the transcribed RNA, skipping parts of the sequence, etc. Moreover, the inability to code for a protein useful to an organism hardly exhausts other possible functions pseudogenes may have.

Furthermore, there is a growing body of evidence that Alu (a SINE) sequences are involved in gene regulation, such as in enhancing and silencing gene activity, or can act as a receptor-binding site — this is surely a precedent for the functionality of other types of pseudogenes. Future studies on the one million Alu copies scattered in the human genome should reveal further regulatory functions of these elements.

The persistence of pseudogenes is in itself additional evidence for their activity. This is a serious problem for evolution, as it is expected that natural selection would remove this type of DNA if it were useless, since DNA manufactured by the cell is energetically costly. Because of the lack of selective pressure on this neutral DNA, one would also expect that ‘old’ pseudogenes should be scrambled beyond recognition as a result of accumulated random mutations. Moreover, a removal mechanism for neutral DNA is now known.

Answer 2

Pseudogenes were once thought to be totally silent, but we now know that they get expressed infrequently, on the order of one time per day. Pseudogenes represent some of the best evidence for evolution, since they can persist in some lineages as regular (expressed) genes and be silent in others.