About Genetic Variation

**3**

**Chapter 1**

**1. Introduction**

Introductory Chapter: Genetic

*Rafael Trindade Maia and Magnólia de Araújo Campos*

Genetic diversity is usually defined as the number of genetic characteristics (alleles and genotypes) in a species [1]. In this context, analyzing the genetic diversity in populations is essential to understand evolutionary and adaptative process for most species [2]. The genetic diversity is also very useful to implement conservation strategies and crop management. This is also the source of disease resistance of

Genes are DNA fragments that encodes some biological information, usually coding a protein or a RNA. Genes can be represented as a sequence of nucleotides that can be expressed in a living organism. Most genes have small nucleotide sequence differences among individuals. These differences are called genetic polymorphism [3]. Some of these polymorphisms may affects how proteins works and how the proteins interacts with subtracts and other proteins. The different gene

The genetic diversity has three different sources: mutation, recombination and immigration of genes. Mutation is the driving force of genetic variation and evolution. There are three types of DNA mutations: base substitutions (also called point

The point mutations are also subdivided in three groups: (1) Silent mutations: when the nucleotide substitution does not change the aminoacid in the polypeptide sequence; (2) Missense mutations: when occurs aminoacid change, that can be classified in conservative (when the change results in an amino acid from the same physical–chemical group) and non-conservative (when the change results in a different physicochemical aminoacid group); (3) Non-sense mutations: when the

Single mutations are very important in population genetics and evolution. They are the mainly source of DNA polymorphic sites, which provides information for many inferences and analysis such as nucleotide and haplotype diversity, allelic diversity, genetic distance, heterozygosity, etc. These parameters are very important to elucidate evolutionary process in populations across time and space. Genes with high levels of polymorphism can be applied to genetic population studies, while genes with moderate and low polymorphic levels can be used for phylogeographic

natural populations, as it is the font of drug resistance by many pathogens.

forms caused by genetic polymorphisms are called alleles.

nucleotide modification results in a stop codon (**Figure 2**).

mutations), deletions and insertions (**Figure 1**) [4].

**2. Base substitutions (point mutations)**

and phylogenetic inferences [5].

Variation - The Source of

Biological Diversity

## **Chapter 1**
