**1. Introduction**

Over the past 20 years, forensic genetic analysis has become the main method for kinship determination and human identification when working with human biological traces and unknown corpses.

DNA identity can be determined 99% of the time (9), but it depends, first of all, on the number and types of studied genetic markers. Traditional forensic DNA analysis is based on autosomal and sex chromosomes STRs polymorphism and sequencing of the non-coding region of mitochondrial DNA. The effectiveness of using these markers varies in different samples due to the state of DNA preservation, especially in samples that have undergone significant changes under the influence of external conditions, such as extreme temperatures (fire), prolonged water exposure or decay in the corpse.

Short Tandem Repeat (STR) analysis is based on DNA typing of specific microsatellite loci with 2 to 7 base pairs length of core units repeat both in autosomal and sex chromosomes.

Due to the high variability in alleles and genotype distribution among unrelated individuals, autosomal STRs DNA analysis serves as an effective human identification tool. The more STR markers are investigated, the more informative individual profiles can be obtained, and the less likelihood coincidence that can be observed. What is more, constant location at specific loci in the genome promotes their stability for a long time even under unfavorable DNA preservation conditions.

Y-chromosomal STRs (Y-STR) are used to determine the presence of male DNA in mixed biological traces. However, the degree of Y-STR preservation is much lower than for autosomal STR and this fact is especially noticeable in the analysis of highly degraded DNA samples. However, Y-STR can be very useful in the determination of paternal lineage relationships and these data can be used as supplementary information to autosomal profiles.

Mitochondrial DNA (mtDNA) markers are significantly better preserved in biological traces compared to autosomal loci (especially in bones) due to their smaller size and multicopy per cell. That is why the study of mtDNA in degraded samples is more often successful. However, there is a significant disadvantage of only mtDNA analysis because of its maternal inheritance. Therefore in order to obtain a complete genetic profile, both types of markers (autosomal and mitochondrial) should be used.

Beside the different stability of described genetic markers, the degree of DNA preservation in biological traces plays a key role in the effectiveness of forensic genotyping and this fact is especially important in DNA profiling of bones and corpse's fragments after putrefactive changes during personal identification analysis [1].

#### **2. DNA profiling efficiency in human remains**

Identification of skeletal human remains rightfully belongs to the category of most complicated molecular genetic analysis. This is due, first of all, to the difficulties in DNA extraction from bones with various degradation degree as well as different DNA amount in specific bone cell types [2, 3].

When there is only part of a body, even the smallest bone fragments can be very useful to determine:


Special traces analysis will assist to answer two questions, but genetic analysis is the only method that allows determination of the kinship between unidentified human remains and probable relatives.

There are various methods and kits for genetic identification that depend on each laboratory's capacity but it is important to obtain all possible genetic marker profiles from the each DNA sample.

For example, obtaining only mitochondrial DNA profile cannot be an objective proof in personal identification because the same mtDNA profile will be found in all maternal relatives, as well as in persons who have a very distant relationship with the deceased. The same applies to the Y-chromosome profile since all male relatives

**57**

**Figure 1.**

*Reliability and Reproducibility of DNA Profiling from Degraded Samples in Forensic Genetics*

will have the same Y-chromosome haplotype, as well as men who are very distantly

In international expert practice, there are no official recommendations as to what types of bones should be analyzed by preference. It is known that long tubular bones both from lower and upper limbs as well as ribs and teeth more often provided for forensic genetic analysis. But there are several assumptions: first of all, it is not always possible to collect all bone remains from the crime scene and secondly

Over 350 fragments from unidentified corpses were analyzed in our laboratory. Our data show that ribs and their fragments were more often sent for genetic analysis (114 cases (32%)); in 83 cases (23%) lower limbs (mainly femurs) were analyzed. The bones of the upper limbs (29 cases/8%), teeth (21 cases/6%) and skull fragments (15 cases/4%) were also found suitable for genetic analysis. Only a few cases of sternum, clavicle, vertebrae, phalanges, heel bone, a spongy bone

Soft tissues can also be an additional source of DNA. According to our data, muscles usually go along with bones and in very rare cases as independent objects

were chosen by an expert-geneticist. However, it is noteworthy that in all these

of DNA and its state of preservation would not correlate with the bone type [9].

Herein, we describe the results of our experience for genetic profiling of differ-

Stable genetic profiles were obtained in more than 80% of analyses of ribs and their fragments. Moreover reliable results were obtained in DNA samples extracted

Muscles were examined in 69 cases (19%), and what is more, in 49 cases, tissues

The reliability of DNA profiles in human remains varies significantly. According to Jakubowska et al., DNA is better preserved in the sternum (90–100% recovery), in lower extremities bones (80–90%), in the lower jaw and teeth, worst - in pelvis, ribs and shoulder girdle bones [7]. These data are somewhat contradictory because different laboratories use their own equipment and reagents for DNA extractions that can affect the final DNA profiling results. Besides, the degree of DNA preservation in bones is influenced by many physical and chemical factors both of exogenous and endogenous nature [8]. In addition, bone cells - osteocytes – carrying basic genetic information, are located unevenly along the length of the tubular bone. That is why the amount

fragment, pelvic bone and liver (total 8% of all cases) were analyzed.

because of its quick destruction due to putrefactive changes (**Figure 1**).

Therefore, only a complex of molecular genetic profiles will give valuable evidence in skeleton fragments or the whole human body identification, especially when working with degraded DNA. It will allow a significant reduction in the probability error, which in turn, can minimize errors in the probability assessment

*DOI: http://dx.doi.org/10.5772/intechopen.98300*

excavated bones may belong to different persons.

cases a stable genetic profile was obtained.

*Femur with the fat wax indicating muscle tissue degradation.*

ent bone types and tissues.

**2.1 Ribs**

related to the deceased [4].

in identification results [5, 6].

#### *Reliability and Reproducibility of DNA Profiling from Degraded Samples in Forensic Genetics DOI: http://dx.doi.org/10.5772/intechopen.98300*

will have the same Y-chromosome haplotype, as well as men who are very distantly related to the deceased [4].

Therefore, only a complex of molecular genetic profiles will give valuable evidence in skeleton fragments or the whole human body identification, especially when working with degraded DNA. It will allow a significant reduction in the probability error, which in turn, can minimize errors in the probability assessment in identification results [5, 6].

In international expert practice, there are no official recommendations as to what types of bones should be analyzed by preference. It is known that long tubular bones both from lower and upper limbs as well as ribs and teeth more often provided for forensic genetic analysis. But there are several assumptions: first of all, it is not always possible to collect all bone remains from the crime scene and secondly excavated bones may belong to different persons.

Over 350 fragments from unidentified corpses were analyzed in our laboratory. Our data show that ribs and their fragments were more often sent for genetic analysis (114 cases (32%)); in 83 cases (23%) lower limbs (mainly femurs) were analyzed. The bones of the upper limbs (29 cases/8%), teeth (21 cases/6%) and skull fragments (15 cases/4%) were also found suitable for genetic analysis. Only a few cases of sternum, clavicle, vertebrae, phalanges, heel bone, a spongy bone fragment, pelvic bone and liver (total 8% of all cases) were analyzed.

Soft tissues can also be an additional source of DNA. According to our data, muscles usually go along with bones and in very rare cases as independent objects because of its quick destruction due to putrefactive changes (**Figure 1**).

Muscles were examined in 69 cases (19%), and what is more, in 49 cases, tissues were chosen by an expert-geneticist. However, it is noteworthy that in all these cases a stable genetic profile was obtained.

The reliability of DNA profiles in human remains varies significantly. According to Jakubowska et al., DNA is better preserved in the sternum (90–100% recovery), in lower extremities bones (80–90%), in the lower jaw and teeth, worst - in pelvis, ribs and shoulder girdle bones [7]. These data are somewhat contradictory because different laboratories use their own equipment and reagents for DNA extractions that can affect the final DNA profiling results. Besides, the degree of DNA preservation in bones is influenced by many physical and chemical factors both of exogenous and endogenous nature [8]. In addition, bone cells - osteocytes – carrying basic genetic information, are located unevenly along the length of the tubular bone. That is why the amount of DNA and its state of preservation would not correlate with the bone type [9].

Herein, we describe the results of our experience for genetic profiling of different bone types and tissues.

#### **2.1 Ribs**

*Forensic Analysis - Scientific and Medical Techniques and Evidence under the Microscope*

ity for a long time even under unfavorable DNA preservation conditions.

in mixed biological traces. However, the degree of Y-STR preservation is much lower than for autosomal STR and this fact is especially noticeable in the analysis of highly degraded DNA samples. However, Y-STR can be very useful in the determination of paternal lineage relationships and these data can be used as supplemen-

Mitochondrial DNA (mtDNA) markers are significantly better preserved in biological traces compared to autosomal loci (especially in bones) due to their smaller size and multicopy per cell. That is why the study of mtDNA in degraded samples is more often successful. However, there is a significant disadvantage of only mtDNA analysis because of its maternal inheritance. Therefore in order to obtain a complete genetic profile, both types of markers (autosomal and mitochondrial) should be used. Beside the different stability of described genetic markers, the degree of DNA preservation in biological traces plays a key role in the effectiveness of forensic genotyping and this fact is especially important in DNA profiling of bones and corpse's fragments after putrefactive changes during personal identification

Identification of skeletal human remains rightfully belongs to the category of most complicated molecular genetic analysis. This is due, first of all, to the difficulties in DNA extraction from bones with various degradation degree as well as

When there is only part of a body, even the smallest bone fragments can be very

Special traces analysis will assist to answer two questions, but genetic analysis is the only method that allows determination of the kinship between unidentified

There are various methods and kits for genetic identification that depend on each laboratory's capacity but it is important to obtain all possible genetic marker

For example, obtaining only mitochondrial DNA profile cannot be an objective proof in personal identification because the same mtDNA profile will be found in all maternal relatives, as well as in persons who have a very distant relationship with the deceased. The same applies to the Y-chromosome profile since all male relatives

sex chromosomes.

analysis [1].

useful to determine:

1.The fact of the death;

2.The nature of the death; and

human remains and probable relatives.

profiles from the each DNA sample.

tary information to autosomal profiles.

**2. DNA profiling efficiency in human remains**

different DNA amount in specific bone cell types [2, 3].

3.Relationships with living relatives and so on.

Short Tandem Repeat (STR) analysis is based on DNA typing of specific microsatellite loci with 2 to 7 base pairs length of core units repeat both in autosomal and

Due to the high variability in alleles and genotype distribution among unrelated individuals, autosomal STRs DNA analysis serves as an effective human identification tool. The more STR markers are investigated, the more informative individual profiles can be obtained, and the less likelihood coincidence that can be observed. What is more, constant location at specific loci in the genome promotes their stabil-

Y-chromosomal STRs (Y-STR) are used to determine the presence of male DNA

**56**

Stable genetic profiles were obtained in more than 80% of analyses of ribs and their fragments. Moreover reliable results were obtained in DNA samples extracted

**Figure 1.** *Femur with the fat wax indicating muscle tissue degradation.*

from rib fragments after fire and in exhumed corpse bones. In 2% of cases a partial profile was obtained, which made it possible to compare the unidentified corpses with close relatives. In 18% of studied cases DNA profile was not determined.
