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- Human genetic variation;
Editor who approved publication: Professor Henrik Druid. DNA obtained from biological samples is able to individualize this material by direct comparison of short tandem repeats genetic profile, obtained from biological samples of unknown origin to a reference sample profile. One of the major limitations of this approach is the need for a reference sample for comparison.
Numerous studies seeking to understand the relationship between certain polymorphisms and certain phenotypic characteristics are increasing and have generated promising results in aiding forensic sciences. The process of inferring externally visible characteristics EVCs with forensic purpose — eg, the color of skin, iris and hair, height, facial features, and male baldness pattern — from biological samples is known as forensic DNA phenotyping FDP.
Therefore, FDP provides more details about the subject to which a given biological sample belongs, without the need for a reference sample for comparative analysis. Some ethical and legal aspects should be taken into account so that this new technology does not promote segregation or ethnic persecution of certain population groups. Despite this, several real cases have benefited from these methods to orientate investigations to identify both suspects and victims.
Human identification based on genetic profiles obtained from DNA polymorphisms short tandem repeats [STRs] is considered to be the gold standard among forensic science techniques. STRs are polymorphisms generated by a sequence in tandem of copies of small DNA segments ranging from 2 to 6 base pairs.
The most informative STRs may present more than a dozen alleles, and thousands of these polymorphisms have already been identified in humans; some estimations point to the existence of about one million STRs distributed among the human genome. The main advantage of STR markers is due to their high allele diversity, making such markers highly informative.
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The most polymorphic STRs have a high discriminating power probability that two randomly selected individuals have distinct genotypes and low probability of match probability that two randomly selected individuals have identical genotypes. There are situations in which biological material from the crime scene is so degraded that DNA samples obtained are not feasible of obtaining enough data for an accurate identification.
In face of such difficulties using traditional STR markers protocols in some situations, various researches have allowed the use of genetic predictions of externally visible characteristics EVCs to be of assistance in police investigations, in both tracking suspects and identifying victims. Several advances in genetics appear to have identified potentially useful markers for the prediction of various physical characteristics. In an attempt to obtain information about the physical features of individuals from DNA extracted from biological material, such as blood drops, hair strands, or small body fragments, the scientific community has intensively researched the association between genetic markers and physical traits.
Some studies have already evaluated the existence of polymorphisms associated with skin, hair and eye color, facial forms, height, and baldness. In this context, it is expected that the genotyping of such genetic markers in crime scene evidence, or in an unidentified body, can contribute significantly to increase the accurate information on the physical characteristics of those involved.
Eye color can be considered as one of the human traits with the most color variability, ranging from light shades of blue to dark shades of brown or black, through intermediate colors such as gray, hazel, yellow, and green. However, intermediate eye colors are still a problem, requiring further research to identify new genetic variants, since the accuracy in their predictions is still much lower when compared with blue and brown eyes. Another debated aspect contemplates gender as a possible influencing factor in the determination of eye pigmentation.
It has been observed that women tend to have darker eyes predominantly brown and green than men predominantly blue and gray in some European countries. Hair color, as well as eye and skin colors, is among the most noticeable EVCs with a wide range of phenotypes. Among several genes involved in the melanogenesis process, MC1R was one of the first to demonstrate a strong discriminating power for red hair, fair skin, and freckles. However, current hair prediction models face a challenge: the accurate prediction of hair colors from individuals who have had hair color changes throughout life eg, darker hair after childhood.
Most studies do not contemplate the sampling of younger individuals, or question adult subjects about distinct phenotypes in early childhood. Therefore, prediction models are only elaborated with phenotypic information observed in adults, without taking into account informative markers for age-dependent phenotypes, partially explaining the lower accuracy value for blond hair only A study done with young individuals found that hair darkening usually occurs between 6 and 13 years of age and that HIrisplex model incorrectly predicts hair phenotypes for those individuals who were blond only during early childhood, advising for the need to identify new markers that could reduce this error rate.
Skin color has been one of the most complex pigmentation phenotypes studied. It is believed that the skin pigmentation variability emerged as an evolutionary response to the intensity of ultraviolet radiation among different planet regions. Regions closer to the Equator line, with higher luminous intensity high UV , would present a higher selective pressure, keeping dark skin with high frequency, while more distant regions, with less luminous intensity, would exert less selective pressure, allowing the appearance of lighter skin tones. While associations found in admixed populations did not have the same discriminatory power in more homogeneous populations, such as Europeans, 28 other studies developed using homogeneous populations could not differentiate skin colors between discrete groups of Asian, African, and Native Americans.
Taking into account this evolutionary obstacle, a global prediction model was developed based on 36 markers distributed among 16 pigmentation genes. Until , only a few genes have been described as associated with human height. Subsequent association studies were performed in in which 54 loci with direct correlation with height variation were observed and in , increasing the number of genetic markers to and subsequently reaching almost markers in Even with significant increase in the number of height-related variants, there are still no significant values for prediction tests.
The face morphology is studied from the distances between facial landmarks, as nostrils width, lips width, distance between eyes and face height. Some of the genetic markers associated with facial features are initially found in syndromes and facial deformities diseases studies such as cleft palate, cleft lip, and other craniofacial dysplasias.
Some of these markers are then correlated to craniofacial development and consequently linked to the normal variation of facial shape. However, similar to height determination, each of these genetic markers seems to have a small contribution toward the total face morphology. The approach used by Claes et al, 43 based primarily on data obtained from admixed populations, employs a first step in which the sample ancestry and gender are used to create a base-face, in which data from 24 SNPs will subsequently be used, to convey nose, lips, face roundness, jaw, chin, and supraorbital crest information to this primary face.
Other studies also found significant associations with facial width, eyebrow width, distance between eyes, columella inclination, nose bridge width, nostril width, and mouth shape. Together, these five SNPs have the best association values to date, with Using a different approach from those previously shown here SNP typing mostly , epigenetics studies using DNA methylation detection technologies have been shown to be useful to the age estimation of an individual.
The age estimation has great importance in the forensic context, since it is complementary to the data obtained by the EVCs mentioned here: besides reducing the number of suspects by predicting the age group of the sample donor, it can also complement the obtained facial composite. Some specific DNA markers can bring information about the ancestral composition of an individual, allowing their biogeographic contributions to be detailed Africa, Europe, Asia, Amerindian.
However, information about ancestry cannot be used solely as a criterion for determining the appearance of an individual. This is especially noticeable in admixed population samples in which AIMs demonstrate that there is no direct correlation between appearance ethnicity and ancestral biogeographic origin. In view of the various legal issues surrounding the sample collection from suspects for comparison, an advantage of DNA phenotyping approach is that it is more focused on obtaining genetic profiles from crime scene samples, thus not harming dignity or integrity rights.
In addition, EVCs are publicly available features and therefore would not involve privacy issues. However, all those individuals who share the characteristics of a facial composite may be interviewed and required to donate samples for comparison to the crime sample in question. In these cases, it is necessary to raise questions about harassment that certain groups with a determined physical characteristic could suffer from the moment a phenotype is obtained from evidence.
One must question whether such individuals will receive any protection, since they will now belong to a group of suspects solely by their physical appearance. Therefore, it should be noted if safety of such groups is being preserved to the detriment of investigation and public safety objectives, and if new legal and ethical regulations should be created to preserve the integrity and intimacy of people involved in DNA phenotyping-based investigations.
Attention should also be drawn to the use of markers that are neutral in relation to ancestry, since information from some AIMs may be erroneously associated to certain phenotypes, resulting in ethnic persecution. Seven years later, police contracted a private DNA phenotype company, which obtained a facial composite predicting a male subject with light brown skin, brown-hazel eyes, and black hair.
The new DNA facial composite led investigation to the crime scene neighboring property, a wildlife sanctuary, where police found a suspect with matching characteristics. After a voluntary sample donation, Hugo Giron-Polanco was arrested since a DNA comparison showed him and the semen sample found on the victim shared the same STR profile with a ,,, match probability. Toronto Police Service has already submitted several cold case samples to private DNA phenotyping services, assisting to change the original direction of the investigations, although no actual arrests occurred.
On May 15, , the German state of Bavaria approved a law for police to analyze DNA samples and predict hair, eye, and skin color in addition to ancestry. These same DNA predictions have already been used in the Netherlands, France, UK, Canada, and several US states, although some of these countries have no precise laws regarding the practice. EVCs prediction can also be very useful in disaster victim identification and identification of missing persons, when no close relatives or antemortem samples exist for comparison. Forty-nine bone and teeth samples from World War II victims found in Slovenia had their DNA extracted and were typed for hair and eye pigmentation genetic markers.
All 49 samples had a successful prediction of eye and hair color, two of the predictions being confirmed by the living sister of two of the victims. In the future, computers may even be able to search composites generated from DNA obtained from biological evidences against government databases or even photos from social media platforms.
Even if this system does not find a perfect match, at least it will be able to narrow down the subjects of interest. The limitation of current DNA forensic techniques is expected to be overcome and new technologies to be developed allowing police investigations to find unknown suspects more quickly through DNA information from crime scenes. Furthermore, the European DNA Profiling EDNAP Group is responsible for promoting meetings and developing collaborative comparison exercises to promote critical evaluations between laboratories around the world, aiming to test the reliability and consistency of new forensic DNA technologies.
So far, EDNAP has tested the IrisPlex System reproducibility between 21 laboratories, considering it to be successful 64 and has recently been evaluating the age prediction through DNA methylation analysis data not published. Although several studies cited here have shown significant phenotype—genotype association Table 1 , it should be noted that each target population has its own genetic background, and extrapolation of these data should be done with caution.
Each set of genetic markers associated to a certain phenotype should be carefully evaluated in additional populations with a different genetic background from those originally studied. Table 1 Summary of main EVCs and some associated genetic markers and references. As most studies are conducted in more genetically homogeneous populations, these found associations should be confirmed in admixed populations when possible, since these populations may present several challenging factors to already established associations, such as population stratification.
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When association studies are done in multiple populations, it is possible to elucidate similarities and differences in genetic structure, limiting candidate regions for new variants identification. Research still needs to be performed to confirm data obtained in diverse global populations and check if none of the associations found are due to ancestry or other populational background in addition to discovering new associations of physical characteristics.
However, despite the many ethical and legal issues that still permeate this subject, the high statistical accuracy of most of these studies makes them viable for practical use in forensic routine. Butler JM.
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Amsterdam, Boston: Elsevier Academic Press; An Introduction to Forensic Genetics. Bond JW. Value of DNA evidence in detecting crime. J Forensic Sci. Forensic aspects of mass disasters: strategic considerations for DNA-based human identification. Leg Med Tokyo. Walsh SJ. Recent advances in forensic genetics.
New Method of Identifying Family Related Skulls
Expert Rev Mol Diagn. Eye colour: portals into pigmentation genes and ancestry. Trends Genet. IrisPlex: a sensitive DNA tool for accurate prediction of blue and brown eye colour in the absence of ancestry information. Forensic Sci Int Genet. Croat Med J. The effect of gender on eye colour variation in European populations and an evaluation of the IrisPlex prediction model.
Further evidence for population specific differences in the effect of DNA markers and gender on eye colour prediction in forensics. Int J Legal Med.
Zvonka Zupanic Slavec (Author of New Method of Identifying Family Related Skulls)
Further development of forensic eye color predictive tests. Developmental validation of the IrisPlex system: determination of blue and brown iris colour for forensic intelligence. Gene-gene interactions contribute to eye colour variation in humans. J Hum Genet. Softcover reprint of the original 1st ed. Seller Inventory LIB Condition: Brand New. In Stock. Seller Inventory x Book Description Springer.
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