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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 • ANEUPLOIDY – MISSING/EXTRA CHROM. • POLYPLOIDY – EXTRA SETS ie. P. Kewensis 2N = 36 from hybridization (2N = 18) Translocation – relocation of groups of base pairs from one part of the genome to another (usually bet. 2 nonhomologous chromosomes…can lead to leukemia) DNA MUTATIONS 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) • X-linked • Fragile X syndrome • CGG repeats 200-1000 times vs 50X for norm Leads to mental retardation (abnormal nerve cell dendrites) DNA MUTATIONS • SILENT – same amino acid • MISSENSE – diff’t a.a. • NONSENSE – stop codon • FRAMESHIFTING Missense Sickle cell anemia Base pair sub GAG (Glu) changed to GTG (Val) … Or Nonsense lethal (base pair sub) RAS mutation • th 12 codon in DNA GGC gen Gly th Mutant 12 codon GTC gen Val Affects RAS’s ability to hydrolzye GTP to GDP...Sig? – Deletion – removal of 1 or more bp (leads to frameshifting …very serious) – Insertion – addition of 1 or more bp (see above) 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” 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 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 RPL21 • Ribosome Protein family = 80 genes • RPL21 140 pseudogenes • Genes become pseudogenes if they incur: a)Loss of promoter b)Loss of introns c)Mutations in the gene (deletions, insertions, non-sense) Lineages diverged 75 mya Mouse 14 / Human 8 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 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! 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 Normal, Founder, Hotspot Sickle Cell – Founder Achondroplasia – Hot Spot 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 Founder Mutations • Persist because they offer advantages as heterozygotes • Ie Cystic Fibrosis (CFTR gene) prot. from diarrhea • Sickle Cell (HbS gene) prot. from Malaria 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) MC1R MUTANTS • Mutants in MC1R gene • 1 in 25 million chance of generating black coloration • A population of 100,000 mice will generate 1 black form every 100 years • ROCK POCKET MICE lava flows vs sandy areas DUPLICATIONS • EXPANSION OF GENETIC INFORMATION ie Globin Family; ADH vs OXYTOCIN • ALLOWS FOR FINETUNING OF 1 GENE without “harm” to other OPSIN DUPLICATIONS • LAMPREY 5 • BIRDS, REPTILES,FISH 4 • MAMMALS 2 (blue, yellow) • OLD WORLD MONKEYS, APES , HUMANS - 3 • MAMMALS LOSS OF OPSINS DURING THE DINOSAUR ERA • MAMMALS WERE NOCUTURNAL • TRICHROMATIC • RED, GREEN, BLUE • RED/GREEN – X chrom RED OPSIN (560 nm) GREEN OPSIN (530 nm) • RED/GREEN 98% similar; same chromosome • 15 amino-acid diff; 3 account for most of 30 nm difference