Biology Reference
In-Depth Information
and the screwworm (
Wright and Pal 1967; King 1975; Robinson 1971; Sokoloff
1966, 1977; Steiner et al. 1982; Heckel 1993; Goldsmith et al. 2005; Gooding and
Krafsur 2005
). Genetic studies of honey bees and silk moths were pursued with
the goal of improving these beneficial insects (
Rinderer 1986, Robinson 1971,
Tazima 1964, Tazima et al. 1975
). By 2012, the completed genome sequences of
a variety of insects and mites had been sequenced, allowing much more sophis-
ticated analysis of their biology, ecology, behavior, and genetics. Genomes
sequenced to date include the honey bee
Apis mellifera
, silk moth
Bombyx
mori
, pea aphid
Acyrthosiphon pisum
, the parasitoid
Nasonia
, the mosquitoes
Anopheles gambiae
and
Aedes aegypti
, the flour beetle
Tribolium castaneum
,
the twospotted spider mite
Tetranychus urticae
, the tick
Ixodes scapularis
, red
imported fire ant
Solenopsis invicta
, the human body louse
Pediculus humanus
,
and the monarch butterfly
Danaus plexippus
. Plans are under way to sequence
5000 arthropod genomes now that sequencing has become relatively inexpen-
sive using next-generation sequencing methods (
Robinson et al. 2011
). Genome
sequencing and the results obtained are discussed in Chapter 7.
Analyzing genes, development, and genetic systems from insects other than
Drosophila melanogaster
could help solve both basic and applied problems
because
D. melanogaster
may be a highly specialized insect with unique genetic
characteristics.
4.6 Dynamic Insect Genomes
Until recently, the eukaryote genome was considered to be relatively stable,
with every cell having the same DNA sequences in the same amounts and in the
same location. Genomes were perceived to respond slowly to evolutionary pres-
sures. It is now apparent that somatic genomes are more diverse than previously
imagined, with polyteny, polyploidy, and gene amplification occurring in differ-
ent tissues at different developmental stages in the organism (
Edgar and Orr-
Weaver 2001
). It is also clear that DNA can move within the nuclear genome via
a wide array of transposable elements (TEs).
DNA has been found in interesting structures outside the nuclear chromo-
somes and mitochondrion, but their significance is unresolved. For example,
covalently closed circular DNAs that seem to be derived from chromosomal DNA
have been found in cell cultures of
Drosophila
(
Gaubatz 1990
). Much of this cir-
cular DNA is middle-repetitive chromosomal DNA and may be associated with
gene amplification during development or with DNA rearrangements during
aging (
Gaubatz 1990
). Some circular DNA molecules in
D. melanogaster
embryos
apparently contain 5S ribosomal RNA genes, satellite DNA, or histone genes
(
DeGroote et al. 1989
).
