Pseudogene

Pseudogenes are believed to have resulted as mutation to an original functioning coding sequence. One scenario for the evolution of a pseudogene is that the environment of an organism changes sufficiently such that the gene product is no longer necessary for the survival of that organism (for example an enzyme may not be required at a different temperature). This means that there is then no longer selection pressure to maintain this sequence, and organisms can continue to survive by accumulating mutations in the sequence. For example, mutations in certain nucleotide positions can result in a premature "stop" codon which leads to a shorter than normal polypeptide chain protein, which is incapable of folding into a functioning protein.