Introduction to Genetic Analysis (Introduction to Genetic Analysis (Griffiths))

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Chapter 14: The Dynamic Genome—Transposable Elements I) Transposable elements and mobile elements—can move to new positions within the same chromosome or to a different chromosome A) Retrotransposons—transposon that uses reverse transcriptase to transpose through an RNA intermediate B) Largest component (50%) of the human genome II) McClintock’s experiment A) In one strain of maize, chromosome 9 broke very frequently at a particular locus due to two genetic factors 1) Dissociation (ds)—located at site of break 2) Activator (Ac)—unlinked genetic factor needed to activate the breakage B) Ac and Ds actually mobile elements C) For chromosome breaking strain, chromosome that breaks at or near Ds loses its end containing wild-type alleles of C, Sh, and Wx genes 1) Chromosome fragment is lost through breakage at the Ds locus causes the recessive alleles on the homologous chromosome to be expressed producing a colorless kernel 2) Insertion of Ds in the C gene creates a colorless corn kernel, excision of Ds from the C gene through the action of Ac in cells and their mitotic descendents allows color to be expressed again, producing a spotted phenotype a) Ds prevented the expression of C b) Unstable phenotype—spotted kernel, frequent reversion either somatically or germinally or both due to the interaction of transposable elements with the host gene III) The leaving element is excised or transposed A) Autonomous elements—require no other elements for mobility, encode info necessary for own movement and movement of unlinked nonautonomous elements B) Nonautonomous elements—need an autonomous element to move C) Element family—one or more autonomous elements and the nonautonomous members that can be mobilized IV) Transposable elements in prokaryotes A) Bacterial insertion sequences (IS elements)—segments of bacterial DNA that can move from one position on a chromosome to a different position on the same chromosome or a different chromosome 1) When appear in middle of genes, interrupt sequence and inactivate expression of the gene 2) Can also block expression of other genes in the same operon if genes are
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Chapter 14 - Chapter 14: The Dynamic Genome-Transposable...

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