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CHANGES IN THE GENOME

CHANGES IN THE GENOME. MUTATIONS A) chromosomal changes B) DNA seq. changes Note: Mutation rate in transcription much higher than during replication…why?. New source of alleles  variety Double-edged sword! Can be used to trace evolutionary history. CHROMOSOMAL MUTATIONS.

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CHANGES IN THE GENOME

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  1. CHANGES IN THE GENOME • MUTATIONS • A) chromosomal changes • B) DNA seq. changes Note: Mutation rate in transcription much higher than during replication…why?

  2. New source of alleles  variety • Double-edged sword! • Can be used to trace evolutionary history

  3. CHROMOSOMAL MUTATIONS

  4. ANEUPLOIDY – MISSING/EXTRA CHROM. • POLYPLOIDY – EXTRA SETS ie. P. Kewensis 2N = 36 from hybridization (2N = 18)

  5. Translocation – relocation of groups of base pairs from one part of the genome to another (usually bet. 2 non-homologous chromosomes…can lead to leukemia)

  6. DNA MUTATIONS

  7. Autosomal Condition Huntington’s – chromosome 4 Normal allele  6-35 CAG repeats Huntington’s  40-150+ CAG repeats • Causes Neurodegeneration • Blocks acetyl-transferases in brain cells (reg. gene expression)

  8. X-linked • Fragile X syndrome • CGG repeats 200-1000 times vs 50X for norm Leads to mental retardation (abnormal nerve cell dendrites)

  9. DNA MUTATIONS • SILENT – same amino acid • MISSENSE – diff’t a.a. • NONSENSE – stop codon • FRAMESHIFTING

  10. Missense Sickle cell anemia  Base pair sub GAG (Glu) changed to GTG (Val) … Or Nonsense lethal (base pair sub)

  11. RAS mutation • 12th codon in DNA GGC  gen Gly Mutant 12th codon GTC  gen Val Affects RAS’s ability to hydrolzye GTP to GDP...Sig?

  12. Deletion – removal of 1 or more bp (leads to frameshifting …very serious) • Insertion – addition of 1 or more bp (see above)

  13. Transposons-Barbara McClintock • Are moveable genetic elements. • DNA sequence can jump into a gene rendering it inactive • Contain enzyme transposase. • Most are retrotransposons (use reverse transcriptase to conv. mRNA to DNA for incorporation into the gene) • Ie 800 bp insertion in starch-related enzyme in peas  “wrinkling”

  14. PSEUDOGENES • “false” or “dead genes” • Produced 2 ways: a) during division an extra copy is inserted into genome in a new location b) reverse transcription

  15. Reverse transcription • Retrotransposition is the insertion of DNA into Genome • Carried out by LINES (long interspersed nuclear elements) that sweep up DNA and mRNA (then retrotransposed) for insertion into genome

  16. RPL21 • Ribosome Protein family = 80 genes • RPL21 140 pseudogenes

  17. Genes become pseudogenes if they incur: • Loss of promoter • Loss of introns • Mutations in the gene (deletions, insertions, non-sense)

  18. Lineages diverged 75 mya

  19. Mouse 14 / Human 8

  20. GULO Pseudogene • Functional in rodents • Nonfunctional in primates • GULO makes an enzyme in the pathway for making vitamin C • Explains why we need vit-C

  21. EVOLUTIONARY IMPORTANCE • Useful molecular clocks as they are not constrained by selection – 99% human/rat gene sim vs few% in pseudogene sim • Shows primate lineage lost many olfactory genes (300 human pseudogenes still functional in rats) – tradeoff with better vision!

  22. FOUNDER MUTATIONS • Mutation arises in the founder and is passed on • Can be classified as a founder by examining surrounding sequences…if the same it’s a founder mutation / if not it’s a Hot-Spot mutation

  23. Normal, Founder, Hotspot

  24. Sickle Cell – FounderAchondroplasia – Hot Spot

  25. Value of Founder…. • Can be dated by examining DNA surrounding founder mutation (the Haplotyope) • Haplotyopes get shorter with time (crossing over) and can be used as a clock and to determine ancestral lineages

  26. Founder Mutations • Persist because they offer advantages as heterozygotes • Ie Cystic Fibrosis (CFTR gene)  prot. from diarrhea • Sickle Cell (HbS gene)  prot. from Malaria

  27. MUTATIONS AND EVOLUTION • MUTATIONS CAN…. 1.Occur in non-coding reg. 2. Be silent in coding region 3. Be shielded (diploid) 4. Affect gene (pos/neg)

  28. MC1R MUTANTS • Mutants in MC1R gene • 1 in 25 million chance of generating black coloration

  29. A population of 100,000 mice will generate 1 black form every 100 years • ROCK POCKET MICE  lava flows vs sandy areas

  30. DUPLICATIONS • EXPANSION OF GENETIC INFORMATION ie Globin Family; ADH vs OXYTOCIN • ALLOWS FOR FINE-TUNING OF 1 GENE without “harm” to other

  31. OPSIN DUPLICATIONS • LAMPREY 5 • BIRDS, REPTILES,FISH 4 • MAMMALS 2 (blue, yellow) • OLD WORLD MONKEYS, APES , HUMANS - 3

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