Chapter 4 - Chapter 4 Diagnostics of Linkage I Several...

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Chapter 4: Diagnostics of Linkage I) Several types of chromosome maps are necessary A) Important b/c: 1) Gene position is crucial info needed to build complex genotypes 2) Knowing position of a gene provides way of zeroing in on its structure/function 3) Can deduce evolutionary genetic mechanisms through which these genomes diverged B) Chromosome map—shows gene positions (loci) 1) Recombination-based maps—map loci of genes that have been identified by mutant phenotypes showing single-gene inheritance 2) Physical maps—show genes as segments arranged along the long DNA molecule that constitutes a chromosome II) Recombination maps—assembled 2-3 genes at a time through linkage analysis A) Linked—loci of genes are on the same chromosome 1) Tend to be inherited as a package 2) Do not assort independently—produce recombinant frequency of <50% B) Phenotypes of offspring from test cross reveal the alleles contributed by the gametes of dihybrid parent C) Cis conformation (two dominant/wild type alleles on same homolog)—AB/ab or + +/ab D) Trans conformation—on different homologs—Ab/aB or +b/a+ E) Linkage symbolism 1) Alleles on same homolog have no punctuation b/t them 2) Slash separates two homologs 3) Alleles written in same order on each homolog 4) Genes on different chromosomes are separated by semi-colon 5) Genes of unknown linkage separated by a dot III) Linked genes still show some recombinants through A) Crossing over—chromosomes break and exchange parts 1) Crossover products—two new combinations 2) Chromatids (duplicated chromosomes) tend to participate in crossing over 3) Correlation b/t genetic event of the appearance of recombinants and chromosomal event of crossing over 4) Results from breakage and reunion of DNA 5) Takes place at four chromatid stage B)
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