For example the lysozyme gene was duplicated and evolved into the α lactalbumin gene in mammals
Lysozyme is an enzyme that helps protect animals against bacterial infection
α-lactalbumin is a nonenzymatic protein that plays a role in milk production in mammals
II. Acquisition of new genes from other species
Comparisons of bacterial and archaeal genome sequences suggest that lateral gene transfer has been a major event in the evolution of prokaryotic genomes
Conjugation , for example, enables plasmids to move between bacteria and frequently results in the acquisition of new gene functions by the recipients
A second process for DNA transfer between prokaryotes , transformation , is more likely to have had an influence on genome evolution.
Non-coding DNA and Genome Evolution
Transposable elements and genome evolution
Transposons can initiate recombination events between chromosomes or between different sites on the same chromosome that lead to genome rearrangements.
Origins of introns
Self-splicing introns evolved in the RNA world and have survived ever since without undergoing a great deal of change
Origins of GU-AG introns:
‘ Introns early’ states that introns are very ancient and are gradually being lost from eukaryotic genomes.
‘ Introns late’ states that introns evolved relatively recently and are gradually accumulating in eukaryotic genomes.
‘ introns early’ called ‘exon theory of genes’ Minigenes became exons and the DNA sequences between them became introns .
Introns early prediction
‘ Introns early’ predicts that there should be a close similarity between the positions of introns in homologous genes from unrelated organisms , because all these genes are descended from an ancestral intron-containing gene
First evidence obtained supported ‘introns early’.
A study of vertebrate globin proteins concluded that each of these comprises four structural domains,
The first corresponding to exon 1 of the globin gene, the second and third to exon 2, and the fourth to exon 3
Leghemoglobin gene of soybean was shown to have an intron at exactly the expected position (splits the second and third domains )
Comparing genome sequences provides clues to evolution and development