Sitemap

health advisory Hospital Doctor Yu 2007-11-8 19:08:12

Answers:

Clearly, some parts of the genome change more easily than others in the course of evolution. A segment of DNA that does not code for protein and has no significant regulatory role is free to change at a rate limited only by the frequency of random errors. In contrast, a gene that codes for a highly optimized essential protein or RNA molecule cannot alter so easily: when mistakes occur, the faulty cells are almost always eliminated. Genes of this latter sort are therefore highly conserved. Through 3.5 billion years or more of evolutionary history, many features of the genome have changed beyond all recognition; but the most highly conserved genes remain perfectly recognizable in all living species.

These latter genes are the ones that must be examined if we wish to trace family relationships between the most distantly related organisms in the tree of life. The studies that led to the classification of the living world into the three domains of bacteria, archaea, and eucaryotes were based chiefly on analysis of one of the ribosomal RNA subunits鈥攖he so-called 16S RNA, which is about 1500 nucleotides long. Because the process of translation is fundamental to all living cells, this component of the ribosome has been well conserved since early in the history of life on Earth.

From alberts et al.

---

because it does not change in coding from one generation to the next (unlike DNA, which goes through Recombination).

as a result you can use it to track changes in each generation -

---