Biology Reference
In-Depth Information
Kaminker et al. (2002)
subsequently analyzed the
Drosophila
genome and
identified 85 known and eight novel families of TEs, with copy numbers varying
from 1 to 146. Most of the TEs were partial elements, and many were localized
in the regions near the centromeres. Most TEs were found outside genes, and
some were found nested within other elements of the same or different classes.
Depra et al. (2009)
found that
hobo
(class II) transposons and
hobo
-related ele-
ments are expressed as early developmental genes in
Drosophila
embryos and
in the nervous system because regulatory sequences similar to those in develop-
mental genes exist in
hobo
sequences. Thus, TEs may provide potentially benefi-
cial developmental and evolutionary changes by acting as regulatory elements.
As noted in Chapter 4, the telomeres of
Drosophila
chromosomes are formed by
non-long terminal repeat retrotransposons. These retrotransposons are named
Het-A
,
TART
, and
TAHRE
, and they are found in many species of
Drosophila
.
These elements transpose onto chromosome ends to form long arrays that
extend the chromosome and compensate for loss (
George et al. 2010
).
7.10.4 Surprises in the
Drosophila
Genome
Several unexpected results were found. First, early analyses of the
Drosophila
genome suggested there are
≈
13,600 genes, slightly fewer than the number
found in the nematode
C. elegans
(
Adams et al. 2000
).
Drosophila melanogaster
was expected to have
≈
30,000 genes.
Drosophila
probably has
>
13,600 genes
because it has a relatively large number of overlapping genes (
Ashburner 2000
),
and many protein-coding genes undergo alternative splicing.
Immediately after obtaining the
D. melanogaster
genome sequences, a com-
parison was made to the genomes of
C. elegans
and
S. cerevisiae
in the context
of cellular, developmental, and evolutionary processes (
Rubin et al. 2000
). The
comparisons indicated
Drosophila
had many undiscovered genes, despite hav-
ing been the subject of extensive genetic analyses. Annotation of the
Drosophila
genome also indicated this insect is surprisingly relevant to the study of genes
and metabolic pathways involved in tumor formation and development in
humans (
Potter et al. 2000, Chintapalli et al. 2007
). Many of the well-studied
signal pathways in tumor development in humans are conserved between flies
and humans, and at least 76
Drosophila
genes are homologs to mammalian can-
cer genes and are under intensive study. Furthermore, 178 (62%) of 287 known
human-disease genes seem to be conserved in
Drosophila
, including genes caus-
ing neurological (Alzheimer's disease, Huntington's disease, Duchenne muscular
dystrophy, and juvenile-onset Parkinson's disease), renal, cardiovascular, meta-
bolic, and immune diseases and malformation syndromes (
Fortini et al. 2000
).
