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Genome Evolution

Genome Evolution. Evolution of Gene clusters. Why are genes are arranged in clusters?. 45S. ITS. 28S. NTS. ETS. 18S. ITS. 28S. NTS. Many genes are arranged in groups of related genes along a chromosome - gene clusters Eukaryotic ribosomal RNA genes: tandem repeats. Gene Families.

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Genome Evolution

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  1. Genome Evolution Evolution of Gene clusters

  2. Why are genes are arranged in clusters? 45S ITS 28S NTS ETS 18S ITS 28S NTS • Many genes are arranged in groups of related genes along a chromosome - gene clusters • Eukaryotic ribosomal RNA genes: tandem repeats

  3. Gene Families • Related genes may be organized is several clusters at different locations These are known as gene families e.g. Globin genes

  4. Gene Families

  5. Gene duplication and misalignment • The misalignment of genes during recombination is the most likely cause of gene duplication and clustering. • Once repeats exist the probability of misalignment increases.

  6. Misalignment - simple case A B A B B A B A

  7. Misalignment - Globin

  8. But not all DNA codes for genes • Single copy DNA can be used as a rough guide to the amount of the DNA that actually codes for genes. • % of single copy DNA ranges from 95% in some arthropods to 12% in an Amphibian (newt) • Human have 64% SC DNA

  9. Types of repetitive DNA • Tandem Repeats • Microsatellites (repeats 2-5 b pairs) 100 repeats per loci • Minisatellites (repeats 15 base pairs) average length 500-2000 nucleotides • Satellite DNA (5-100 base pairs) found in blocks of 1000 or more repeats

  10. Types of repetitive DNA • Scattered repeats - Longer sequences (100 or more base pairs) scattered through the genome usually as single copies

  11. Selfish DNA - tandem repeats • Most non-coding DNA is selectively neutral • It will passively replicate and may be duplicates as with coding tandem repeats • It will continue to accumulate until it’s mass slows the cell cycle then it will be selected against

  12. Selfish DNA - Scattered Repeats • Transposable elements • Transposition by reverse transcription - disrupts genome and increase number of copies of self • Transposition without reverse transcription - disrupts genome

  13. Selfish DNA - Scattered Repeats • Origin - are they ancient and very successful virus?

  14. The C-factor Paradox • Why is there excess DNA? • Selfish DNA provides an attractive hypothesis to solve this question. • It would also explain why apparently functionless DNA is functionless

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