Over the last decade, the usage of X chromosomal short tandem repeat (STR) markers has increased dramatically in the forensic field. This current study was conducted to analyze the genetic of (X-STR) frequencies in Arab Iraqi male population. The purpose of this study was to explore at the frequency of 12 (X-STR) haplotypes in the Iraqi population as a reference data source for individual identification. As allele frequency, the distributions of observed alleles and genotype frequencies for the 200 unrelated Arab Iraqi males were demonstrated. The results of the present study revealed the high and low frequency of these alleles. Our findings revealed that the DXS7424 locus of Iraqi males showed the range between 0.02 and 0.34 with high frequency for allele 16 and low frequency for alleles 11 and 12. Relative to the DXS7424 locus, previous study by Nakamura Y and Minaguchi K., 2010 showed that the alleles in Japanese population were 12, 13, 14, 15, 16, 17, and 18 and frequency ranged from 0.011 to 0.445 with similar high frequency (0.445) for allele 16 .
According to the above results concerning HPRTB locus, the allele frequency ranged from 0.05 to 0.37 with high and low frequency for allele 11 and allele 9 respectively. The study by Hameed et al. 2015 conducted in Iraq found that the alleles in Iraqi population were 7, 8, 9, 10, 11, 12, 13, 14, 15, and 16 and frequency ranged from 0.002 to 0.436 with high frequency (0.436) for allele 13 . This finding could be related to the use of argus 8X-STR specific X-STR kits, whereas in this study, the authors employed multiplex PCR from 12 loci as described by Nakamura Y and Minaguchi K ., 2010 .
In the DXS8377 locus, the high, low, and rare frequency alleles were for allele 46, alleles 52, 53, and allele 55 respectively with frequencies ranged from 0.05 to 0.16. However, the findings by Poetsch et al. 2005 discovered that the alleles at this locus were 39, 40, 41, 42, 43, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, and 56 in German population and the allele 51 had a high-frequency percentage (0.138) .
Regarding to the GATA31E08 locus, the high and low allele frequency alleles were observed in allele 11 and 7 respectively and the allele frequency ranged from 0.01 to 0.365. It was found by Nakamura Y and Minaguchi K., 2010 that the most prevalent alleles in the Japanese population were 7, 8, 9, 10, 11, 12, 13, and 14, with a frequency ranging from 0.001 to 0.307, with allele 11 having the highest frequency (0.307) .
In the present study, the DXS7423 locus had a high and low allele frequency showed in allele 14 and 17 with a rare allele showed in allele 12. Similarly, previous studies done by Al-Snan et al. 2019 and Hameed et al. 2015 reported that the allele 14 at DXS7423 locus emerged as a high-frequency allele with allele frequency 0.462 and 0.409, and this locus exhibit low polymorphic alleles [22, 23]. The study done by Nakamura Y and Minaguchi K., 2010 showed that the alleles in Japanese population was 13,14,15,16 with frequency ranged from 0.005 to 0.608 with high frequency (0.608) for allele 15 .
As a result, the DXS8378 locus had a high and low allele frequency for allele 10 and allele 14 with a range from 0.01 to 0.365. In a contrast with the present study, previous studies in Iraq and Germany revealed that the allele 11 having the highest frequency (0.371 and 0.374) respectively .
The DXS9895 locus showed the high allele frequency for allele 15 and low frequency for allele 13 with a rare allele reported for allele 11, 18, and 19. Such observation suggested by Poetsch et al. 2005 upon the DXS9895 locus found that the allele 24 having a high frequency .
The allele frequencies at DXS10074 locus ranged from 0.005 to 0.41 and the allele 15.2 appeared in high frequency and allele 12.2 and 17 in low frequency and as a rare allele found in allele 13.2, 14, and 19.2. A previous study done in Iraqi and Turkish population revealed that the high frequency allele at the DXS10074 locus was 15 [22, 24].
The allele frequencies at DXS6809 locus ranged from 0.03 to 0.27, and the allele 35 appeared in a high frequency while the low frequency appeared in allele 36. Such a result of previous study in Japan revealed that the allele repeats in Japanese population was 26, 29, 30, 31, 32, 33, 34, 35, 36, and 37 and frequency range from 0.003 to 0.309 with a high frequency for allele 33 .
The allele frequencies at DXS7133 locus ranged from 0.02 to 0.46 and the allele 11 appeared in a high frequency while the low frequency was found in alleles 15 and 16. The findings obtained by Nakamura Y and Minaguchi K., 2010 conducted in japan showed that the allele repeat in Japanese population was 9, 10, 11, and 12 and frequency range from 0.06 to 0.7 with a high frequency for allele 9 .
The allele frequencies at DXS101 locus ranged from 0.015 to 0.22 and the allele 25 appeared in high frequency with low frequency observed in allele 22 and 29. The result of previous study in Germany showed that the allele repeat in German population was 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, and 30 and frequency range from 0.03 to 0.2 with high frequency for allele 24 .
The allele frequencies at DXS6807 locus ranged from 0.005 to 0.405 and the allele 11 appeared in high frequency while the low allele frequency showed in allele 17 and allele 18 found as a rare allele. A prior investigation carried out in japan showed that the allele repeat in Japanese population was 11, 12, 13, 14, and 15 and frequency range from 0.08 to 0.370 with similar a high frequency for allele 11 .
Rare alleles are polymorphic alleles that occur in less than 1% of the population. However, the frequency of detecting functional uncommon alleles was highly dependent on the sample size .
The power of discrimination (PD) is the chance that choosing two individuals randomly would not have matching DNA profile. The current study found the PD value ranged from 0.663 for DXS7423 locus and 0.9066 for DXS8377 locus. This result is close to Iraqi study that showed the DXS7423 locus had 0.522 of PD value  and an Italian study the PD value was 0.913 for DXS8377 locus .
Polymorphism information content (PIC) is evaluated by the markers ability to identify polymorphism in the population based on the number of alleles detected and the frequency of their distribution. Therefore, PIC determines the marker’s discriminatory capability, basically depending on the number of recognized (identified) alleles and their frequency of distribution . The result of the present investigation revealed that the PIC for all twelve loci were appeared more than 0.5, indicating good informativeness of all X-STR markers.
In order for novel alleles to be noted in DNA profiles, consideration should be given to these new alleles for forensic science recommendations with a view to being included in the DNA database, and in order to assign frequency to estimate the probability of a specific DNA profile across a population of interest (random match probability) [27, 28].
The distribution occurrence is another measure to examine the frequencies of the most common occurrence genotypes in order to identify the usefulness for particular set of DNA markers would therefore be the least powerful in terms of being able to differentiate between two unrelated individuals [29, 30].
The X-STR loci become main completely and alternative uses for forensic application especially, kinship testing, miss distress, and more efficient use degraded DNA and is widely used in many complicated cases.
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