Biology Reference
In-Depth Information
Grand Duke Ludwig
4th of Hesse
Princess Alice (2nd daughter
of Queen Victoria)
Louise of
Hesse-Cassel
Tsar
Nicholas 2nd
Tsarina
Alexandra
Princess
Victoria
Tsar
Nicholas
2nd
Alice of
Battenburg
Georgij
Romanov
Alexei
Maria Tatiana Olga
Anastasia
Prince Philip
Duke of
Edinburgh
Duke of Fife
Xenia
Cheremeteff-
Sfiri
(a)
(b)
Figure 13.2
The family tree of the Romanov royal family: (a) shows the maternal lineage of
the Tsarina and her children which provides a direct link to Prince Philip and (b) illustrates the
maternal lineage of Tsar Nicholas, linking him to two living maternal relatives, the Duke of Fife
and Xenia Cheremeteff-Sfiri. The squares represent males and the circles represent females, the
transmission of the relevant mtDNA type is in red
from the unknown sample has to be compared with a reference profile. In the case
of a crime scene investigation, the reference sample will be from a suspect. In the
case of human identification, a sample taken from a maternal relative or a personal
artefact such as a toothbrush can be used [38].
The first step is to turn the information into a more manageable form. The data
after sequencing consist of upwards of 350 DNA bases from both HV-I and HV-II
and around 150 bases from HV-III. Once the sequencing data have been checked to
ensure that there is confidence in the sequence data and no errors, it is compared
with the Cambridge Reference Sequence (CRS) [11, 12]. The CRS was the first
complete sequence of the mtDNA genome to be published in 1981. Differences
between the questioned sequence and the CRS are noted and only these differences
are recorded. Table 13.1 shows an example of where a HV-I profile generated from
a set of human remains is compared with profiles generated from three reference
samples. The mtDNA profile is called a haplotype.
Homoplasmy and heteroplasmy
Normally an individual contains only one type of mtDNA: this is termed homoplasmy
(Figure 13.3). Mutations will inevitably occur within some of the thousands of copies
of mtDNA within a cell and if these mutated copies of the genome were passed on
to future generations, a mixture of different mtDNA genomes would occur. The
process that maintains homoplasmy as the norm is not precisely understood but at
some point a genetic bottleneck occurs before the formation of a mature oocyte [40].
The bottleneck allows only a few mtDNA molecules to pass into the oocyte during
its formation [41, 42], thereby reducing the possibility of passing on a mixture of
wild type and mutant genomes.
