Biology 1001A Lecture Notes - Lecture 6: Transposable Element, Genetic Recombination, Transposase
24 Jan 2017
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Inheritance of Difference
Section 9.4 and 12.4
Mobile Elements
o All organisms appear to contain particular segments of DNA called
mobile elements, that can move from one place to another
• They cut and paste sections of DNA using a type of recombination
that does not necessarily require homology
• Sometimes called jumping genes, these elements move from place
to place within the genome of a given cell
o Mobile elements are also known by the more specific term transposable
elements (TEs)
• Their mechanism of movement, involving nonhomologous
recombination, is called transposition
o Transposition usually occurs at a low frequency in either of two ways,
depending on the type of element
1. a cut and paste process, in which the TE leaves its original location
and transposes to a new a location
2. a copy and paste process, in which a copy of TE transposes to a
new location, leaving the original TE behind
o for most TEs, transposition starts with the contact between the TE and the
target site
• this also means that TEs do not exist free of the DNA in which they
are integrated; hence, the popular name jumping genes is actually
inaccurate
o TEs are important because of their genetic changes they cause
o They produce mutations by transposing into genes and knocking out their
functions, and they increase or decrease gene expression by transposing
into regulatory sequences of genes
o As such, TEs are biological mutagens that increase genetic variability
o Some bacterial TEs insert randomly, at any point in the DNA, whereas
others recognize certain sequences as “hot spots” for insertion and insert
preferentially at these locations’
o The two major types of bacteria TEs are insertion sequences (ISs) and
transposons
• Insertion sequences are the simplest TEs
• They are relatively small and contain only genes for their
transposition, notably the gene for transposase, an enzyme that
catalyzes some of the recombination reactions for inserting or
removing the TE from the DNA
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