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Vol. 14(27), pp. 2175-2178, 8 July, 2015
DOI:10.5897/AJB2015.14457
Article Number: 2E48C3F54052
ISSN 1684-5315
Copyright © 2015
Author(s) retain the copyright of this article
http://www.academicjournals.org/AJB
African Journal of Biotechnology
Review
Y-Chromosome short tandem repeat, typing
technology, locus information and allele frequency in
different population: A review
Muhanned Abdulhasan Kareem1, Ameera Omran Hussein2 and Imad Hadi Hameed2*
1Babylon University, Centre of Environmental Research, Hilla City, Iraq.
2Department of Molecular Biology, Babylon University, Hilla City, Iraq.
Received 29 January, 2015; Accepted 29 June, 2015
Chromosome Y microsatellites seem to be ideal markers to delineate differences between human
populations. They are transmitted in uniparental and they are very sensitive for genetic drift. This review
will highlight the importance of the Y- Chromosome as a tool for tracing human evolution and describes
some details of Y-chromosomal short tandem repeat (STR) analysis. Among them are: microsatellites,
amplification using polymerase chain reaction (PCR) of STRs, separation and detection and advantages
of X-chromosomal microsatellites.
Key words: Forensic, population, review, STR, Y- chromosome.
INTRODUCTION
Microsatellites are DNA regions with repeat units that are
2 to 7 bp in length or most generally short tandem
repeats (STRs) or simple sequence repeats (SSRs)
(Ellegren, 2000; Imad et al., 2014). The classification of
the DNA sequences is determined by the length of the
core repeat unit and the number of adjacent repeat units.
It may contain several hundred to thousands (Butler,
2012) of these. Tandem repeats occur in the form of
iterations of repeat units of almost anything from a single
base pair to thousands of base pairs. Mono-, di-, tri- and
tetranucleotide repeats are the main types of
microsatellite, but repeats of five (penta-) or six (hexa-)
nucleotides are usually classified as microsatellites as
well. DNA can be used to study human evolution.
Besides, information from DNA typing is important for
medico-legal matters with polymorphisms leading to more
biological studies (Walkinshaw et al., 1996). Since the
STR markers are important for human identification
purposes (Rui et al., 1996) the number of repeats can be
highly variable among individuals and can be used for
identification purposes. There are three types of repeat
patterns for STRs. Two or more adjacent simple repeats
*Corresponding author. E-mail: imad_dna@yahoo.com.
Author(s) agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0
International License
Abbreviations: STR, Short tandem repeat; PCR, polymerase chain reaction; SSRs, simple sequence repeats; PAGE,
polyacrylamide gel electrophoresis; CE, capillary electrophoresis; SNP, single nucleotide polymorphism; Y-DNA, Y-chromosome
DNA; mtDNA, mitochondrial DNA.
Figure 1. Relative positions of 23 Y-STR loci available in the
PowerPlex® Y23 System. The six new loci are shown in bold font.
PAR1 and PAR2 are pseudo-autosomal regions on the tips of the Y
chromosome that recombine with the X chromosome. The shaded
region around AMEL Y can sometimes be deleted, causing loci such as
DYS458 to be missing from an otherwise full Y-STR profile. DYS391 is
located a sufficient distance away to avoid deletions affecting AMEL Y
(Butler, 2012).
are considered a compound repeat. Units of similar
length are called simple repeats (Budowle, 1995; Butler
et al., 2009; Mohammed and Imad, 2013).
Chromosome Y microsatellites or short tandem repeats
(STRs) seem to be ideal markers to delineate differences
between human populations for several reasons: (i) They
are transmitted in uniparental (paternal) fashion without
recombination, (ii) they are very sensitive for genetic drift,
and (iii) they allow a simple highly informative haplotype
construction (Kayser et al., 1997). Also for forensic
applications, this ability to differentiate distinct Y
chromosomes makes Y- STRs an advantageous addition
to the well characterized autosomal STRs. For a number
of forensic applications, Y- STRs could be preferred to
autosomal STRs. Especially in rape cases where (i) the
differential extraction was unsuccessful, (ii) the number of
sperm cells is very low, (iii) due to vasectomy epithelial
cells instead of sperm cells from the ejaculate of the
perpetrator have to be analyzed, and (iv) the perpetrator,
due to a familial relationship shares many autosomal
bands with the victim, Y- STRs could provide crucial
evidence. Also, in the case of male-male rape or rape
cases with multiple perpetrators Y- STRs could lead to
essential qualitative evidence. In all such cases Y- STRs
facilitate a simple and reliable exclusion of suspects.
Unlike autosomal STR markers, Y-STR markers are
linked on the same chromosome and there is no genetic
recombination between the markers (Figure 1).
Therefore, unlike for autosomal STRs, the Hardy-
Weinberg equation is not suitable for determining the
frequency of a genotype from the frequency of the alleles
at each locus (Beleza et al., 2003; Dupuy et al., 2004;
Imad et al., 2015a; Mohammed et al., 2015). To
determine the frequency of a particular Y-STR profile, the
profile must be searched against different databases for a
possible match, and these databases must be large
enough to accurately represent the frequencies of the
haplotypes present in the population of interest. Thus, as
more Y-STR samples are typed and contributed to a
database the more useful the database will become.
However, at present, the databases are much too small
to enable forensic scientists to attain the level of
2176 Afr. J. Biotechnol.
discrimination provided by autosomal STR analysis
(Ballantyne et al., 2010; Imad et al., 2015b; Muhanned et
al., 2015).
AMPLIFICATION USING POLYMERASE CHAIN
REACTION OF STRs
A billion copies of a given target sequence can be
provided by Polymerase Chain Reaction (PCR) in a fast
in vitro DNA synthesis process. A DNA polymerase may
duplicate to result in specific DNA markers to be
surfaced. dNTPs, Mg++ and a thermal stable DNA
polymerase, (usually Taq polymerase) are five main
chemical components. During the cycling of tem-
peratures, the primers are designed to hybridize to the
specific markers (e.g. STR loci) along the length of the
template. A special DNA polymerase that is heat stable is
used to copy and amplify the genetic markers using the
remaining components after the DNA strands are
separated and the primers bind to the template. This
happens for a given thermal cycle (Del et al., 2009;
Nadine et al., 2010). To analyze the DNA, the process of
28 to 32 heating and cooling cycles, is increased. The
amplification of multiple samples can be done at one
time. In fact in 3 h 96 samples can be amplified in this
manner. The thermal samples contain many sample wells
that allows this to happen when several different loci are
simultaneously amplified in a single tube when multiple
PCR occurs. It has been found lately that even 15
autosomal short tandem repeats (STRs) have been done
at one time using DNA from a very small amount of
contaminated sample.
SEPARATION AND DETECTION
After PCR there must be a process of separation and
detection of the amplified products. A number of ways
can be used to carry out the typing. Among them are (1)
PolyAcrylamide Gel Electrophoresis (PAGE) followed by
silver staining or if the primers are fluorescently tagged,
detection by fluorescent gel scanners and (2) Capillary
Electrophoresis (CE) with laser induced fluorescence.
Based on the fact that it is automated this method has
become popular. No gel is used and samples can be
inserted mechanically. The resolution of the higher
molecular weight loci is usually better than in the PAGE
methods since the DNA traverses the entire length of the
capillary. There are several components that impact DNA
separations within CE systems. Among these are the
polymer used for enabling the separation, the capillary,
the electrophoresis buffer, and the field strength (John et
al., 2004). The objective of the exercise is to introduce a
different dye onto the 5’-(nonreactive) end of each primer
or set of primers (Giusti and Adriano, 1993). The
properties of these dyes are quite unusual. Although
fluoresce in different regions of the spectra they all
excited by a single argon-ion laser tuned to 488 nm. To
determine which dye is present, based on the emission of
each fragment as it passes the detector window, a
multiwavelength analyzer, such as a charged coupled
device (CCD) camera, can then be used. The advantage
of this method allows the analysis of fragments of DNA
that overlap in size as long as they are labeled with
different colors, which fluoresce at different wavelengths.
The STR fragments in the sample are amplified using
primers with fluorescent tags in the most commonly used
analytical method for detecting STRs. There is
fluorescent dye in every new STR fragment made in a
PCR cycle. When light is shown over it, each dye will
emit a different color. Using electrophoresis in automated
“genetic analyzer” machinery the fragments are
separated according to their length. This technology is
developed as a by-product of the technology developed
for the Human Genome Project. That first carried out to
sequence most of the entire genome. In these machines
an electric field is used to extract DNA fragments placed
at one end of the tube through the entangled polymer or
comparable sieving medium. This is done using a long,
narrow tube (a “capillary”). The bigger or bulkier
fragments move slowly in the medium as compared to
the smaller ones. Sending a laser beam through small
glass window in the tube causes it to fluoresce at specific
wavelength as the tagged fragments pass under the light.
A kind of electronic camera records the intensity of light
emitted by the dye. This can be translated into a graph,
which shows a peak as an STR flashes by. Firstly, a
short allele will pass by the window and fluoresce first.
Later a longer fragment will come by, and this will show
another peak on the graph.
HAPLOTYPE DIVERSITY FOR Y-CHROMOSOMAL
STR IN DIFFERENT POPULATIONS
Observed Alleles, PCR Product Sizes, Repeat Structure
and PCR Primer Sequences have been tabulated (White
et al., 1999). The observed numbers of haplotypes and
their frequencies have been tabulated (Table 1).
Haplotypes detected in this study group have been
compared with seven other populations: German (n =
88), Indian (n = 25), Chinese (n = 36), Italians (n = 100)
(Manfred et al., 2001), Mozambican (n = 112) (Alaves et
al., 2003), Japanese (n = 161) (Hara et al., 2007) and
Turkish (n = 280) (Henke et al., 2001). Our data have
also provided additional information to the framework of
variation involving seventeen Y-STR loci as well as a
further contribution to the Y-STR database for Iraq
population. This supports the observations by others
(Jorde et al., 2000) that, especially among European
populations. Y-STRs are very powerful in the detection of
genetic differences between male populations, compared
with autosomal STRs. This can be attributed to the
Kareem et al. 2177
Table 1. Comparison of the haplotypes and haplotype diversity in different human population groups.
Parameter
Iraq1
Tunis2
German3
Italy4
China5
India6
India7
Individuals number
320
105
88
100
36
25
154
Haplotypes number
276
81
77
82
34
16
152
Unique haplotypes
256
67
39
53
28
13
150
Proportion of unique haplotypes
0.93
0.83
0.51
0.65
0.82
0.81
0.98
Non-unique haplotypes
20
14
38
29
6
3
2
Proportion of non-unique haplotypes
0.07
0.17
0.49
0.35
0.18
0.19
0.01
Ratio (unique : non-unique)
13.2
4.88
1.03
1.83
4.67
4.33
98
Haplotypes diversity
0.8392
0.9932
0.9963
0.9941
0.9968
0.950
0.9935
1References: (Imad et al., 2013), 2Reference: (Imen et al., 2005), 3Reference: (Manfred et al., 2001), 4Reference:
(Manfred et al., 2001), 5Reference: (Manfred et al., 2001), 6Reference: (Manfred et al., 2001), 7Reference: (Kuppareddi et
al., 2010).
greater sensitivity of nonrecombining Y-chromosomal
markers to founder effects and genetic drift. A similar
conclusion was reached by Forster et al. (2000), on the
basis of a phylogenetic approach only. The use of Y-
STRs allows the simple construction of highly variable
haplotypes. With these haplotypes, it is possible to
analyze differences in population structure by a
comparison of haplotype diversity and of the number of
population-specific haplotypes.
In the study of molecular evolution, a haplogroup is a
group of similar haplotypes that share a common
ancestor with a single nucleotide polymorphism (SNP)
mutation. Haplogroups pertain to deep ancestral origins
dating back thousands of years. The most commonly
studied human haplogroups are Y-chromosome or (Y-
DNA) haplogroups and mitochondrial DNA (mtDNA)
haplogroups, both of which can be used to define genetic
populations. Y-DNA is passed solely along the patrilineal
line, from father to son, while mtDNA is passed down the
matrilineal line, from mother to both daughter and son.
The Y-DNA and mtDNA may change by chance mutation
at each generation. Therefore pattern H77 shared in
three unrelated males in this study may be descended
from same ancestry.
According to a 2000 study of Y-chromosome sequence
variation human Y-chromosomes trace ancestry to Africa,
and the descendants of the derived lineage left Africa and
eventually were replaced by archaic human Y-
chromosomes in Eurasia. The study also shows that a
minority of contemporary East Africans and Khoisan are
the descendants of the most ancestral patrilineages of
anatomically modern humans that left Africa 35,000 to
89,000 years ago (Collins et al., 1998). Other evidence
supporting the theory is that variations in skull
measurements decrease with distance from Africa at the
same rate as the decrease in genetic diversity. Human
genetic diversity decreases in native populations with
migratory distance from Africa, and this is thought to be
due to bottlenecks during human migration, which are
events that temporarily reduce population size (Manica et
al., 2007; Phillips et al., 2011). Regarding forensic
applications, the unique pattern of Y-DNA in the rest of
samples in present study makes it useful as powerful tool
for discrimination individuals in crimes, rapes and
paternity or log dead people such as in mass graves.
Conflict of interests
The authors did not declare any conflict of interest.
ACKNOWLEDGEMENTS
This research would not have been possible without the
assistance of Assoc. Prof. Dr. Cheah Q. and Prof. Dr.
Issam who have contributed immensely in providing
knowledge and assistance for this study.
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