Biology Reference
In-Depth Information
Figure 3.6
Diagram of the circular DNA molecule from the mitochondria of
Drosophila yakuba
. The
outside circle shows the open reading frames (URF1-URF6 and URF 4 L) that code for subunits of
the respiratory chain NADH dehydrogenase and of the genes coding for cytochrome
b
; cytochrome
c
oxidase subunits I, II, and III; and ATPase subunits 5 and 6. The origin of and direction of rep-
lication are indicated by O and R. The variable A
+
T region is shaded. The arrows indicate the
direction of gene transcription. The tRNA genes are crosshatched and indicated by their single-letter
amino-acid codes. lrRNA and srRNA are the large and small rRNA genes, respectively. The numbers
on the inside of the outer circle are the numbers of apparently noncoding nucleotides that occur
between the genes. The innermost circles indicate restriction fragments produced with the enzymes
indicated (from
Clary and Wolstenholm 1985
).
More detailed investigation of insect mitochondrial genomes may provide
some contradictions to the above-mentioned generalizations. For example,
mitochondrial genomes
>
20 kb have been found in three species of curculionid
beetles (
Pissodes strobi
,
Pissodes nemorensis
, and
Pissodes terminalis
) (
Boyce
et al. 1989
). The large size (30-36kb) in these three
Pissodes
species is due to
