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TEs from the viruses' insect hosts ( Fraser 1985 ). Four families of TEs were found
in the triatomine bug Rhodnius prolixus that feeds on the blood of opossums,
squirrel monkeys, and other vertebrates (including humans, to which it can
transmit Chagas' disease) ( Gilbert et  al. 2010 ). The sequences of the TEs in the
insect and in the vertebrates were very similar, suggesting that host-parasite
interactions are important in horizontal transfer among animals.
New TEs are being found on a consistent basis, and a database of repetitive
elements, including TEs, can be found at the website for the Genetic Information
Research Institute (GIRI) ( Jurka et al. 2005 ).
Thomas et  al. (2010) found that Helitrons (rolling-circle transposons) have
moved horizontally among mammals, reptiles, fish, invertebrates, and insect
viruses. “The presence of horizontally transferred Helitrons in insect viruses
[Bracoviruses], in particular, suggests that this may represent a potential mech-
anism of transfer in some taxa” ( Thomas et  al. 2010 ). Another Bracovirus was
found to have a large DNA transposon ( Maverick ) in it, suggesting that TEs
may transfer from parasitoid insects to their lepidopteran hosts by these viruses
( Dupuy et al. 2011 ).
Yuan and Wessler (2011) analyzed the sequences of the catalytic portion of
all superfamilies of cut-and-paste (class II) TEs in eukaryotes, and they found
that all superfamilies have a common molecular signature and, thus, evolu-
tionary origin. It seems that most superfamilies of cut-and-past TEs originated
before the divergence of eukaryotic supergroups such as green algae, fungi, ver-
tebrates, invertebrates, ciliates, and diatoms ( Feschotte and Pritham 2007 ). All
class II transposons probably rely heavily on horizontal transfer for their propa-
gation and maintenance over evolutionary timescales.
4.10 Highly Repetitive DNA
Highly repeated DNA sequences with a uniform nucleotide composition can,
upon fractionalization of the genomic DNA and separation by density-gradient
centrifugation, form one or more bands that are clearly different from the main
band of DNA and from the smear created by other fragments of a more hetero-
geneous composition. These sequences are called satellite DNA .
Satellite DNA is sometimes described as minisatellite or microsatellite DNA,
depending on the length of the repeated sequences. Microsatellites consist of
tandem repeats of between 1 and 6bp, often in long arrays; like other classes
of repetitive DNA, microsatellites have high mutation rates ( Bachtrog et  al.
1999 ). Satellite DNA can comprise a large fraction of the arthropod genome; for
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