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Genome origin


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genome evolution

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Genome origin

  1. 1. GENOME <ul><li>GENOME ORGANIZATION </li></ul><ul><li>ACQUISITION OF NEW GENES </li></ul><ul><li>ORIGIN OF INTRONS </li></ul>Ms.ruchi yadav lecturer amity institute of biotechnology amity university lucknow(up)
  4. 4. MITOCHONDRIAL GENOME <ul><li>At just 16 569 bp </li></ul><ul><li>Contains just 37 genes . </li></ul><ul><li>13 of these genes code for proteins involved in the respiratory complex </li></ul><ul><li>The other 24 specify non-coding RNA molecules that are required for expression of the mitochondrial genome. </li></ul>
  6. 6. Genome Evolution
  7. 7. Acquisition of New Genes <ul><li>There are two ways in which new genes could be acquired by a genome: </li></ul><ul><ul><li>By duplicating some or all of the existing genes in the genome . </li></ul></ul><ul><ul><li>By acquiring genes from other species </li></ul></ul>
  8. 8. I. Acquisition of new genes by gene duplication <ul><li>By duplication of the entire genome; </li></ul><ul><li>By duplication of a single chromosome or part of a chromosome; </li></ul><ul><li>By duplication of a single gene or group of genes. </li></ul>
  9. 9. Whole-genome duplications can result in sudden expansions in gene number The basis of autopolyploid
  10. 10.   Autopolyploids cannot interbreed successfully with their parents <ul><li>Hugo de Vries, During his work with evening primrose, Oenothera lamarckiana , de Vries isolated a tetraploid version of this normally diploid plant, which he named Oenothera gigas . </li></ul>
  11. 11. Duplications of individual genes and groups of genes have occurred frequently in the past Multigene families are common components of all genomes
  12. 12. Examples of multigene families of nonidentical genes are two related families of genes that encode globins
  13. 13. Human Globin Genes
  14. 14. <ul><li>There are several mechanisms by which these gene duplications could have occurred: </li></ul>
  15. 15. Alterations of Chromosome Structure <ul><li>Humans have 23 pairs of chromosomes, while chimpanzees have 24 pairs </li></ul><ul><li>Following the divergence of humans and chimpanzees from a common ancestor, two ancestral chromosomes fused in the human line </li></ul>
  16. 16. Alterations of Chromosome Structure
  17. 17. Genome evolution also involves rearrangement of existing genes <ul><li>This is possible because most proteins are made up of structural domains. </li></ul><ul><li>Each domain comprise a segment of the polypeptide chain and hence encoded by a contiguous series of nucleotides. </li></ul>
  18. 18. There are two ways in which rearrangement of domain-encoding gene segments can result in novel protein functions .
  19. 19. Domain shuffling: segments coding for structural domains from completely different genes are joined together to form a new coding sequence that specifies a hybrid or mosaic protein
  20. 20. Domain Duplication <ul><li>The α2 Type I collagen has repetitive Gly-X-Y </li></ul><ul><li>It codes for 338 of these repeats, is split into 52 exons , 42 of which cover the part of the gene coding for the glycine-X-Y repeats. </li></ul><ul><li>The number of repeats per exon varies but is 5 (5 exons), 6 (23 exons), 11 (5 exons), 12 (8 exons) or 18 (1 exon). </li></ul><ul><li>Gene have evolved by duplication of exons leading to repetition of the structural domains. </li></ul>
  21. 21. Domain shuffling: Tissue plasminogen activator ( TPA ),
  22. 22. Evolution of Genes with Novel Functions <ul><li>For example the lysozyme gene was duplicated and evolved into the α lactalbumin gene in mammals </li></ul><ul><li>Lysozyme is an enzyme that helps protect animals against bacterial infection </li></ul><ul><li>α-lactalbumin is a nonenzymatic protein that plays a role in milk production in mammals </li></ul>
  23. 23. II. Acquisition of new genes from other species <ul><li>Comparisons of bacterial and archaeal genome sequences suggest that lateral gene transfer has been a major event in the evolution of prokaryotic genomes </li></ul><ul><li>Conjugation , for example, enables plasmids to move between bacteria and frequently results in the acquisition of new gene functions by the recipients </li></ul><ul><li>A second process for DNA transfer between prokaryotes , transformation , is more likely to have had an influence on genome evolution. </li></ul>
  24. 24. Non-coding DNA and Genome Evolution <ul><li>Transposable elements and genome evolution </li></ul><ul><ul><li>Transposons can initiate recombination events between chromosomes or between different sites on the same chromosome that lead to genome rearrangements. </li></ul></ul>
  25. 25. Origins of introns <ul><li>Self-splicing introns evolved in the RNA world and have survived ever since without undergoing a great deal of change </li></ul><ul><li>Origins of GU-AG introns: </li></ul><ul><li>‘ Introns early’ states that introns are very ancient and are gradually being lost from eukaryotic genomes. </li></ul><ul><li>‘ Introns late’ states that introns evolved relatively recently and are gradually accumulating in eukaryotic genomes. </li></ul>
  26. 26. ‘ introns early’ called ‘exon theory of genes’ Minigenes became exons and the DNA sequences between them became introns .
  27. 27. Introns early prediction <ul><li>‘ 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 </li></ul>
  28. 28. First evidence obtained supported ‘introns early’. <ul><li>A study of vertebrate globin proteins concluded that each of these comprises four structural domains, </li></ul><ul><li>The first corresponding to exon 1 of the globin gene, the second and third to exon 2, and the fourth to exon 3 </li></ul><ul><li>Leghemoglobin gene of soybean was shown to have an intron at exactly the expected position (splits the second and third domains ) </li></ul>
  29. 29. Comparing genome sequences provides clues to evolution and development