**7. DNA fingerprinting and human identification**

assemblies using long-read sequencing have revealed that each human genome has approximately 20,000 structural variants, spanning 10 million base pairs, more than twice the number of bases affected by SNVs. New long-read sequencing approaches are needed to meet this challenge, as short-read sequencing technologies only detect 20% of the SVs present in the

DNA-based molecular markers are such powerful tools for mapping human diseases and

Genetic mapping and linkage: The mapping of the human genome has made possible to develop a haplotype map in order to better define human SNV variability. The haplotype map or HapMap will be a tool for the detection of human genetic variation that can affect health and diseases [23]. The HapMap project is far more useful because it will reduce the number of SNVs required to examine the entire genome for association with a phenotype or diseases from the 10 million SNPs that are expected to exist to approximately tag 500,000 SNPs [38]. The first large-scale effort to produce a human genetic map was performed mainly using RFLP; other several projects are underway to identify more markers in humans and to make this data publicly available to scientists worldwide. Many groups that are involved in these massive efforts through DNA polymorphisms discovery resource include the SNP consortium (TSC) http://snp.cshl.org [49, 50]. The reason for the current enormous interest in SNPs is the hope that they could be used as markers to identify genes that predispose individuals to

common, multifactorial disorders by using linkage disequilibrium (LD) mapping.

**6.2. Quantitative trait loci mapping, candidate genes, and complex traits**

"The HapMap Project (http://hapmap.ncbi.nlm.nih.gov/), and other approaches, such as genome wide association studies, have been widely reported for complex polygenic diseases, with some interesting novel genes affecting disease susceptibility now identified. Genome Wide Association; the GWAS has now been used for a large range of traits and diseases e.g.

The identification of genes affecting complex trait is a very difficult task. For many complex traits, the observable variation is quantitative, and loci affecting such traits are generally termed quantitative trait loci (QTL). (SNVs) can be used as genetic markers for constructing high-density genetic maps and to carry out association studies related to complex traits and

Individual response to a drug is governed by many factors such as genetics, age, sex, environment, and disease. The influence of genetic factors on the response of a drug is a known fact.

**6. The major application for DNA-based genetic markers**

discover many multifactorial diseases and disorders.

**6.1. Mapping human diseases and risk prediction**

human genome [45–48].

32 Genetic Diversity and Disease Susceptibility

baldness and eye color" [51, 52].

diseases [14].

**6.3. Pharmacogenetics**

Establishing an individual's identity is one of the uses of DNA sequence information that highlights uniqueness of a particular sample [5], also known as genetic fingerprinting; DNA typing and DNA profiling are molecular genetic methods that enable the identification of individuals using hair, blood, semen, or other biological samples, based on unique patterns in their DNA. This uniqueness in each individual is the basis of human identification at the DNA level, forensic identification, determination of genetic variation, determination of family relationship, and one important instance is identifying good genetic matches for organ or marrow donation. When first described in 1984 by British scientist Alec Jeffreys, the technique used was minisatellites; these sequences are unique to each individual, with the exception of identical twins. Different DNA fingerprinting methods exist, using either restriction fragment length polymorphism (RFLP) or PCR or both. More than 200 RFLP loci have been described in human DNA. Initially, forensic medicine used minisatellite testing; however, this method requires a large amount of material and yield low-quality results especially when only little amount of materials are available. Nowadays, in most forensic samples, the study of DNA is usually performed by microsatellite analysis. The most useful microsatellite for human identification is those with a greater number of alleles, smaller size, higher frequency of heterozygotes (higher than 90%), and low frequency of mutations [43]. Among others, the microsatellite DNA marker has been the most widely used, due to its easy use by simple PCR, followed by a denaturing gel electrophoresis [40]. Each person has some STRs that were inherited from the father and some from mother, useful in paternity testing but however no person has STRs that are identical to those of either parent. The uniqueness of an individual's STR provides the scientific marker of identity and hence is helpful in forensic identification [54]. Genomic and mitochondrial are two types of DNA which are used in forensic sciences. The genomic DNA is found in the nucleus of each cell in the human body and represents a DNA source for most forensic applications. Mitochondrial DNA (mt DNA) is another source of material that can be used; various biological samples such as hair, bones, and teeth that lack nucleate cellular materials can be analyzed with mt DNA [43, 55].

#### **7.1. Sex-chromosome STR testing**

"Majority of the length of the human Y chromosome is inherited as a single block in linkage from father to male offspring as a haploid entity. DNA genetic markers on the human Y chromosome are valuable tools for understanding human evolution, migration and for tracing relationships among males" [43, 56]. "Chromosome X specific STRs is used in the identification and the genomic studies of different ethnic groups worldwide, because the small size of X-chromosome STR alleles; about 100–350 nucleotides, it is relatively easy to be amplified and detected with high sensitivity" [43].

an important role in genome structure, evolution, and diversity. Additional efforts are being placed to develop strategies that would overcome the obstacles in alignment next-generation sequencing data. "Future precision medicine efforts will direct to connect genotypes to phenotypes and distinguish common, from rare or potentially disease linked variants. New long-

DNA Polymorphisms: DNA-Based Molecular Markers and Their Application in Medicine

http://dx.doi.org/ 10.5772/intechopen.79517

35

Other important applications of genetic polymorphism knowledge are improving health care through gene therapy, discovery of new drugs and drug targets, and upgradation of the dis-

Advances in molecular technologies, DNA sequencing technology, and microarray, coupled with novel, efficient computational analysis tools, have made it possible to analyze sequence-

based experimental data, more discoveries, and development at a rapid rate.

Molecular Genetics Unit, Medical Ain Shams Research Institute, Faculty of Medicine,

[1] Daly AK. Pharmacogenetics and human genetic polymorphisms. The Biochemical

[2] Buckingham L. Chromosomal structure and chromosomal mutation. In: Buckingham L, editor. Molecular Fundamentals Methods and Clinical Applications. 2nd ed. Phila-

[3] Ismail S, Essawi M. Genetic polymorphism studies in humans. Middle East Journal of

[4] Rothberg JM, Hinz W, Rearick TM, Schultz J, Mileski W, Davey M, Leamon JH, Johnson K, Milgrew MJ, Edwards M, Hoon J, Simons JF, Marran D, Myers JW, Davidson JF, Branting A, Nobile JR, Puc BP, Light D, Clark TA, Huber M, Branciforte JT, Stoner IB, Cawley SE, Lyons M, Fu Y, Homer N, Sedova M, Miao X, Reed B, Sabina J, Feierstein E, Schorn M, Alanjary M,

read sequencing approaches are needed to meet this challenge."

covery processes with advanced technologies.

The author declares that there is no conflict of interest.

Address all correspondence to: salwateama2004@yahoo.com

Journal. 2010;**429**(3):435-449. DOI: 10.1042/BJ20100522

delphia: F.A. Davis Company; 2012. Chapter 8. ISBN.0-8036-2677-0

**Conflict of interest**

**Author details**

Ain Shams University, Cairo, Egypt

Medical Genetics. 2012;**1**:57-63

Salwa Teama

**References**

#### **7.2. DNA typing and engraftment monitoring**

DNA typing becomes the method of choice for engraftment monitoring, donor cells are examined by following donor polymorphisms in the recipient blood and bone marrow. Although RFLP can efficiently differentiate donor and recipient cells, the detection of RFLP requires the use of southern blot methods, which is too labor intensive and has limited sensitivity for this application, in comparison with small minisatellites or microsatellites that are easily detected by PCR amplification, because of increased rapidity and the 0.5–1% sensitivity achievable with PCR. Sensitivity can be raised to 0.01% using Y-STR, but this approach is limited to that transplant from sex mismatched donor recipient pairs preferably from a female donor to a male recipient [2].

Nowadays, DNA fingerprinting is used as a tool for designing "personalized" medical treatments for cancer patients.
