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REVIEW for FINAL EXAM - Quicknotes - Bio 2C03

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McMaster University
Joe Kim

BIO 2C03 2013 Lecture 6 (Chapter 7) Gene Mapping – Linkage Maps  Exceptions to Mendel’s principle; genes on same chromosome are “linked” and do not sort independently o Can be tested with χ o Linkage can be broken – suggests homologous chromosome able to exchange DNA; physically recombine; crossover  Linkage maps – using recombination frequencies (RF; distance between genes; represents chiasmata frequency); 1% RF = 1 mu (map unit); genes arranged in linearorder (location of gene = gene locus)  If RF<50% pair of genes are linked  Double recombinants – account for by multiplying them by 2; often fewer observed double recombinants than expected o Expected – should be equal to probability of crossover in region 1 and 2 happening at the same time; o Expected = (p of cross over in region 1) x (p of cross over in region 2) o Observed = # from data / total o Discrepancy due to interference  Interference – crossover in one interval reduces probability that additional crossovers will occur nearby o Coefficient of Coincidence (COC) = observed/expected (double crossovers) o Interference = 1 – COC  Cis conformation/coupling (of dominant alleles) AB/ab  Trans conformation/repulsion Ab/aB  % recombinants = % meiotic cells with single crossover/2  Genetic linkage maps underestimate true map distance due to 1) interference (some recombination events do not occur, even if expected) 2) crossover frequency and genetic recombination are not proportional (RF = CF/2); RF=X% for uneven crossovers; RF=0% for even crossovers; <7 mu, RF=CF/2; >7 mu, RF200n long; 14880 in human, >23000 in mouse; 40% human lncRNAs are primate-specific; nuclear  Region of genome that is not transcribed, do not correspond to any gene code, structural RNA or protein structure gene  Intergenic lncRNAs, Genic lncRNAs (exonic (overlap with e, intronic, overlapping)  Lack ORF, expressed at low levels, 39% polyadenylated (enriched in poly(A)RNAs), 98% spliced (canonical splicing junctions),42% have two exons, less conserved than protein-coding genes, great promoter region conservation (suggests regulatory role)  Function – 40% intersect coding genes for proteins involved in transcription regulation, processes and nucleus compartment; enriched in chromatin Chromatin Condensation  Euchromatin vs. heterochromatin Euchromatin Heterochromatin Dispersed (in interphase) Condensed (in interphase) Can be transcribed Cannot be transcribed Predominantly unique DNA sequence; gene rich Repetitive DNA sequence (satellites, derivatives of viruses, transposons etc); g
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