Biology Reference
In-Depth Information
rRNAs, 13 proteins, and 22 transfer RNAs (tRNAs) arrayed in an order that is well
conserved within phyla (
Figure 12.1
). All mtDNAs have at least one noncoding
region, which contains regulatory elements for replication and transcription,
but intergenic sequences are small or absent (
Boore and Brown 1998
). The con-
trol region containing the origin of replication is extremely A
+
T-rich in insects.
Within the insects, the tRNA genes are known to vary in position (
Crozier and
Crozier 1993
). There are thousands of mitochondria in each cell, so mtDNA is
abundant and relatively easy to isolate, even from somewhat-degraded samples.
By contrast, nuclear genes evolve more slowly, which makes it possible to extend
analyses further into the past.
Mitochondrial DNA can be used in analyses of population structure and gene
flow, hybridization, biogeography, and phylogenetic relationships (
Avise et al.
1987, Lang et al. 1999
). The small size, relatively rapid rate of evolutionary
Figure 12.1
Map of mitochondrial DNA of the honey bee,
Apis mellifera
. Genes for tRNAs are
denoted by the one-letter code for their corresponding amino acids. tRNA genes with asterisk are in
a different position compared to the same genes in the mitochondrion of
Drosophila yakuba
. Protein-
coding genes are denoted COI, COII, and COIII for the genes encoding subunits one, two, or three
of
cytochrome c oxidase
,
Cyt b
, for the
cytochrome b
gene and ND4L for the genes encoding subunits 1-6
and 4L of the NADH dehydrogenase system. The AT-rich region containing the origin of replica-
tion is denoted A
+
T. The direction of transcription for each coding region is shown by arrows.
(Redrawn from
Crozier and Crozier 1993
.)
