**Genetic Polymorphism**

**Chapter 1**

**Provisional chapter**

**Polymorphisms**

**Abstract**

**1. Introduction**

**Polymorphisms**

Wasana Sukhumsirichart

Wasana Sukhumsirichart

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

DOI: 10.5772/intechopen.76728

Polymorphism or variation in DNA sequence can affect individual phenotypes such as color of skin or eyes, susceptible to diseases, and respond to drug, vaccine, chemical, and pathogen. It occurs more often than mutations (frequency ≥ 1%). The common polymorphism is single nucleotide polymorphism (SNP) which is a single base change in a DNA sequence that occurs most commonly in the human genome. SNPs have been used as molecular markers in a wide range of studies. Genome-wide association studies (GWAS) searches for SNPs that occur more frequently in person with a particular disease than in person without the disease and pinpoint genes or regions that may contribute to a risk of disease. This topic describes about polymorphisms, SNPs, GWAS, linkage disequilibrium (LD), minor allele frequency, haplotype, method for SNP genotyping, and application of SNPs and genome-wide association study in human diseases and drug development.

**Keywords:** drug development, genome-wide association studies, human diseases,

Phenotype of living organism is controlled by DNA. Variation in DNA sequence or polymorphism may make individual difference such as the differences in phenotype, risk of various diseases, and response to drugs, vaccine, chemical, and pathogen. Polymorphisms commonly occur in nature and related to biodiversity, genetic variation, and adaptation. It helps to maintain variety of forms in a population living in a varied environment [1]. It is preserved by frequency-dependent selection. The polymorphisms in this topic focus on human polymorphisms related to diseases and drug respond. Because the Human Genome Project had been completed, a large number of polymorphisms among the population have been found [2–4]. The most abundant type of the variations is single nucleotide polymorphisms (SNPs), with

polymorphisms, single nucleotide polymorphism, SNPs

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

http://dx.doi.org/10.5772/intechopen.76728

#### **Chapter 1 Provisional chapter**

#### **Polymorphisms Polymorphisms**

#### Wasana Sukhumsirichart Wasana Sukhumsirichart

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.76728

#### **Abstract**

Polymorphism or variation in DNA sequence can affect individual phenotypes such as color of skin or eyes, susceptible to diseases, and respond to drug, vaccine, chemical, and pathogen. It occurs more often than mutations (frequency ≥ 1%). The common polymorphism is single nucleotide polymorphism (SNP) which is a single base change in a DNA sequence that occurs most commonly in the human genome. SNPs have been used as molecular markers in a wide range of studies. Genome-wide association studies (GWAS) searches for SNPs that occur more frequently in person with a particular disease than in person without the disease and pinpoint genes or regions that may contribute to a risk of disease. This topic describes about polymorphisms, SNPs, GWAS, linkage disequilibrium (LD), minor allele frequency, haplotype, method for SNP genotyping, and application of SNPs and genome-wide association study in human diseases and drug development.

DOI: 10.5772/intechopen.76728

**Keywords:** drug development, genome-wide association studies, human diseases, polymorphisms, single nucleotide polymorphism, SNPs

#### **1. Introduction**

Phenotype of living organism is controlled by DNA. Variation in DNA sequence or polymorphism may make individual difference such as the differences in phenotype, risk of various diseases, and response to drugs, vaccine, chemical, and pathogen. Polymorphisms commonly occur in nature and related to biodiversity, genetic variation, and adaptation. It helps to maintain variety of forms in a population living in a varied environment [1]. It is preserved by frequency-dependent selection. The polymorphisms in this topic focus on human polymorphisms related to diseases and drug respond. Because the Human Genome Project had been completed, a large number of polymorphisms among the population have been found [2–4]. The most abundant type of the variations is single nucleotide polymorphisms (SNPs), with

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

more than 9 million reported in public databases [5–7]. In this chapter, the definition of several terms such as polymorphism, minor allele frequency (MAF), allele frequency, haplotype, and linkage disequibrium (LD) is clarified. Moreover, SNPs, genome-wide association study (GWAS), methods to detect SNPs and application of SNPs in association with diseases and drug development are mainly discussed topics.
