pseudo gene

I felt the need to clarify about pseudo gene while I organized an annotation of zymo. Therefore in this post I will review about pseudo gene, what it is and how it was happened.
All information comes from  http://en.wikipedia.org/wiki/Pseudogene


Pseudogene : non-expressed or defunctional relatives of known gene (homology to a known gene, nonfunctionality).
1.homology to a known gene : usually sequence identity is between 40% and 100%.
2.nonfunctionality : if any one of the common processes, which are needed in making functional product from DNA, such as transcription and pre-mRNA processing fails, this will be nonfunctional. In high-throughput psudogene identification, modification of stop codon and frameshifts are the most common factors.


Types and origin of pseudogenes


1. Processed (retrptransposed) pseudogenes : retrotransposition event is common in mammals and in case of human 30%~44% of genome is composed of this. In retrotransposition, mRNA transcript of a gene is reverse transcribed back into DNA become pseudogene. This kind of pseudogene have features of cDNA like poly-A tail, introns spliced out and lack of promoter.

2. Non-processed pseudogenes : Through gene duplication A copy of gene is made and subsequent mutation make them as pseudogene. This kind of pseudogene have the most feature of genes.


3. Disable genes (unitary pseudogene) : same mechanism (i.e. mutation) which make non-processed pseudogene happened to genes without duplication and became fixed in population.