Chapter_13_-_Analysis_of_Genetic_Variati

Chapter_13_-_Analysis_of_Genetic_Variati - 13. Genetic...

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13.0 Nature of genetic variation Genetic variation responsible for the phenotypic difference may arise from: Variation in the gene sequence Variation in other genes that affect expression of the gene Alteration in other cellular components that affect the protein activity
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13.1 Single nucleotide polymorphisms (SNPs) Single nucleotide polymorphism most likely to occur in non-coding regions, and in introns than in exons Change in third position of the codon often leads to no change in the amino acid it codes and is a synonymous substitution or silent mutation Non-synonymous (missense) substitutions which change an amino acid may be innocuous or could be detrimental Change into a stop codon: causes premature termination of protein synthesis and a truncated protein Removal or insert of a base can cause a frameshift mutation Changes in 5’ or 3’ UTR may alter sorting and stability of the mRNA, and recognition sites for interaction with RNA binding proteins Figure 13.1 Codons arising by single- base substitutions from UUA
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13.1 Single nucleotide polymorphisms (SNPs) Having two copies of each gene allows more leeway for evolutionary drift in one allele as long as the other functions normally (eg. carriers of recessive disease genes) Evolutionary drift in one allele can lead to accumulation of mutations that may eventually lead to significant alterations in functions of a protein Individual may be homozygous or heterozygous for any given genetic variation Indentify SNP by sequencing PCR products; can identify variants with primers that only hybridize to the wild- type or mutant allele (allele-specific oligonucleotide probe) Figure   13.2 Point mutations in  RNA polymerase causing rifampicin  resistance in  M.   tuberculosis . The  diagram shows a portion of RpoB  from  M.   tuberculosis . The amino acid  changes shown account, between  them, for over 90 per cent of  rifampicin resistance
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13.2  Larger-scale variations  Outside of point mutations, larger-scale variations include: Insertions (inserted sequence) and Deletions (deleted sequence) = Indels Duplications (duplicated sequence) Transpositions (movement of a DNA segment within the genome of an organism) Inversions (inverted sequence)
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13.2  Larger-scale variations 
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