Biology Reference
In-Depth Information
The mtDNA genome
The human mitochondrial genome is a 16 569 bp circular molecule. It encodes for
22 transfer RNAs (tRNAs), 13 proteins and two ribosomal RNAs (the 12S and
16S rRNAs) [11, 12]. The majority of mitochondrial proteins is encoded by the
nuclear genome as, over hundreds of millions of years, following the formation of
the symbiotic relationship between eubacteria and eukaryote cells, most of the genes
have been transferred from the mitochondrial to the nuclear genome [13]. Analysis of
the human mtDNA genome revealed a very economic use of the DNA and there are
very few non-coding bases within the genome except in a region called the D-loop
(Figure 13.1). The D-loop is the region of the genome where the initial separation, or
displacement, of the two strands of DNA during replication occurs. The regulatory
role of the D-loop has led to the other name by which it is known - the control
region. It is approximately 1100 bp long.
Polymorphisms in mtDNA
The mtDNA genome accumulates mutations relatively rapidly when compared with
the nuclear genome [14]. The high mutation rate
1
is due in part to the exposure of the
HV-I
HV-II
HV-III
Control region
12S rRNA
Cytochrome
b
16S rRNA
mtDNA
16 596 bp
COI
Figure 13.1
The mitochondrial genome is circular and 16 569 bp long. It encodes for 13 proteins
22 transfer RNAs and two ribosomal RNAs. The polymorphic hypervariable regions I and II (HV-I,
HV-II and HV-III) are located within the control region. Other regions of the genome that are
utilized in forensic casework for species identification are the coding regions for the 12S and 16S
ribosomal RNAs, cytochrome
c
oxidase subunit I (COI) gene and cytochrome
b
gene
1
Note: Mutations in the hypervariable regions are normally referred to as 'a base substitution' as they do not have an effect
on any of the products encoded by the mtDNA - for simplicity the term 'mutation' will be used throughout this chapter.
