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University of Toronto St. George
Human Biology
Richard Brown

MGY470 – February 7, 2013 LAST TIME: Development of de novo mutations – if present in germ cell, passed onto offspring Different kinds of mutations Nonsense mediated decay – keep in mind when interpreting individuals’ phenotypes Splicing mutations – increasing percentage of mutations due to splicing Aberrant splicing – notable – can lead to loss or gain of function – Retaining or losing introns/exons – if have regular gene, may retain entire intron so splicing machinery does not see the acceptor, does not see the splice donor – does not splice until get to second splice donor depend to some degree of strength of splice donors and acceptors – weaker = form less well to consensus sequence, leading to unclear outcomes in mutations can lose splice sites; can activate sites; ex. Gene – if pick up cryptic site, have site that will be recognized – dimensions not clear other than able to predict occurance of cryptic site – issue – outcome can be strange – by activating one site – can deactivate another site – see unpredictable outcomes – if have gene with 100kb intron and gene not routinely – well recognized genes, always remain patients without mutations; likely intron variant activated cryptic splice sites – these are not screened routinely, so likely missed splicing mutations silent changes – proven and recognized to be splicing mutations – within exons and introns – there are short segments of sequence that contribute to splicing – either called enhancers or silencers – these sequences bind splicing machinery, ehlp direct machinery to splice donor or acceptor – if interefere, by promoting with binding with enhancer or donor – difficult to predict if do not know what they are – many have been recognized but not all of them – silent mutation – if nucleotide changes from C to T – still code for glycine, predict no amino acid change this is causing a new donor site first prediction based on nucleotide change – silent change BUT not asilent change with regards to splicing – on first look, thought to be silent; but found out to be diseae causing Exon splicing enhancers and silencers – within the sequence – if they interfere with the strength or contribute to or inhibit strength of binding sites – identified largely because have been observed in RNA analysis of tissue – GENETIC DISEASES – physical changes – diseases occur in different frequencies – population vary for various reasons – due to history of particular population, possibly isolated by geography or culture – see unique features of particular disease Also disease frequencies influenced by migration, environmental aspects and pressures Example of cystic fibrosis – Three base pair deletion One mutation that explains many all
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