**3. Recombination**

In eukaryotes, genetic recombination is the aleatory change of genetic material resulting from the meiosis process, also called crossing-over or permutation. This type of recombination consists in break and rejoining homologous regions of pared chromosomes between the Prophase I and Metaphase I from meiosis division (**Figure 3**). Many combinations can be performed among gene exchange between two individuals [7]. Although prokaryotic species does not have chromosomes conjugation is performed by these beings by one of these three process: (a) Conjugation: when the DNA is transferred by tube after cells contact; (b) transduction: the DNA is inserted accidentally from one bacterium to another by a virus; and (c) transformation: when the bacterium receives exogenous DNA from the environment [8].

Recombination is very important because it makes new combinations of the existent alleles. Many effects of the DNA rearrangement can be good for species and populations, once it can improve adaptation. However, some recombination events can be unfavorable if it breaks apart important and beneficial alleles in the sisters chromatids [9]. The recombination rate is positively correlated with

**5**

*Introductory Chapter: Genetic Variation - The Source of Biological Diversity*

nucleotide diversity, which increases genetic variation and resulting in purifying

Nucleotide deletions and insertions are types of mutation that changes the number of DNA base in genome. Deletions changes the base number by removing pieces of DNA and insertions alters the base number by adding pieces of DNA [10]. Often, these kind of mutations results in a gene that encodes a protein that does not function properly (**Figure 4**). When the deletions/insertions change the gene's

Insertions and deletions can be particularly hazardous when occurs in an exon region, which is the coding segment of a gene. Due to multiple new aminoacid after translation, the protein function may be affected [11]. Knowing the rate of insertion–deletion mutations are crucial to understanding evolutionary process, such as natural selection, especially in coding regions due to the protein disruption that is

Gene immigration, or gene flow, is the transfer of genetic material from one population to another by migration of individuals or gametes. This can alter genetic diversity by changing allelic frequencies in populations [12]. Gene flow is essential to prevent population diverging. When gene flow is interrupted by physical (geographical) barriers, allopatric speciation tends to occur. Population gene flow can be

> *Fst Nm* <sup>−</sup> <sup>=</sup> <sup>1</sup> <sup>1</sup>

4

*DOI: http://dx.doi.org/10.5772/intechopen.96499*

deleterious mutations.

**Figure 3.**

usually caused.

**5. Gene immigration**

measured by the formula:

**4. Deletions and insertions**

reading frame they are called *frameshit* mutations.

*Crossing-over scheme in homologous chromosomes. Source: Google Images.*

*Introductory Chapter: Genetic Variation - The Source of Biological Diversity DOI: http://dx.doi.org/10.5772/intechopen.96499*

#### **Figure 3.** *Crossing-over scheme in homologous chromosomes. Source: Google Images.*

nucleotide diversity, which increases genetic variation and resulting in purifying deleterious mutations.

### **4. Deletions and insertions**

*Genetic Variation*

**Figure 1.**

Single mutations are also important for health: many missense mutations can be deleterious and resulting in a disease or metabolic disorder. Another thing to be considered is that single mutations can also provide adaptative vantages such as pathogen resistance, xenobiotic tolerance and fitness improvement [6]. So, detecting point mutations in the organisms can be very useful to implement many strategies such as biodiversity conservation, crop management and infectious disease monitoring.

*Types of point mutations (nucleotide substitution) in DNA molecule. Source: Google Images.*

*Illustrative scheme of DNA mutations types. Source: Google Images.*

In eukaryotes, genetic recombination is the aleatory change of genetic material resulting from the meiosis process, also called crossing-over or permutation. This type of recombination consists in break and rejoining homologous regions of pared chromosomes between the Prophase I and Metaphase I from meiosis division (**Figure 3**). Many combinations can be performed among gene exchange between two individuals [7]. Although prokaryotic species does not have chromosomes conjugation is performed by these beings by one of these three process: (a) Conjugation: when the DNA is transferred by tube after cells contact; (b) transduction: the DNA is inserted accidentally from one bacterium to another by a virus; and (c) transformation: when the bacterium receives exogenous DNA from the environment [8]. Recombination is very important because it makes new combinations of the existent alleles. Many effects of the DNA rearrangement can be good for species and populations, once it can improve adaptation. However, some recombination events can be unfavorable if it breaks apart important and beneficial alleles in the sisters chromatids [9]. The recombination rate is positively correlated with

**4**

**3. Recombination**

**Figure 2.**

Nucleotide deletions and insertions are types of mutation that changes the number of DNA base in genome. Deletions changes the base number by removing pieces of DNA and insertions alters the base number by adding pieces of DNA [10]. Often, these kind of mutations results in a gene that encodes a protein that does not function properly (**Figure 4**). When the deletions/insertions change the gene's reading frame they are called *frameshit* mutations.

Insertions and deletions can be particularly hazardous when occurs in an exon region, which is the coding segment of a gene. Due to multiple new aminoacid after translation, the protein function may be affected [11]. Knowing the rate of insertion–deletion mutations are crucial to understanding evolutionary process, such as natural selection, especially in coding regions due to the protein disruption that is usually caused.

#### **5. Gene immigration**

Gene immigration, or gene flow, is the transfer of genetic material from one population to another by migration of individuals or gametes. This can alter genetic diversity by changing allelic frequencies in populations [12]. Gene flow is essential to prevent population diverging. When gene flow is interrupted by physical (geographical) barriers, allopatric speciation tends to occur. Population gene flow can be measured by the formula:

$$Nm = \frac{\left(\frac{1}{Fst}\right) - 1}{4}$$

#### **Figure 4.**

*Illustrative example of a DNA insertion modifying all the subsequent codons. Source: Google Images.*

Where *Nm* refers to the number of migrants per generation; *Fst* is the degree of genetic differentiation.

When *Fst* is 1, there is a strong differentiation among populations. Gene flow is also very important to reduce genetic drift effects. Due to this particularity, the gene flow is extremely important for conservation genetics.

#### **6. Final considerations**

Genetic diversity is a very important feature of living organisms. It serves for population adapting to environment, once that how higher is the allelic variation, it is more likely that individuals display adaptative characteristics that suits to the environment. So, genetic diversity is essential for species survival.

Molecular markers, amplification and DNA sequencing technologies are improving an incredible advance in access genetic variation. The number of sequences and genomes deposited in the databases grows exponentially, generating an enormous amount of information to be studied and analyzed. The knowledge resulting from this information has innumerous applications and has been promoting a huge revolution in several areas of the biological, agrarian and health sciences. The way we understand, analyze and deal with biodiversity has been intensely modified and deepened by the advancement of genetics. In this context, knowledge about the genetic diversity of organisms will bring solutions to various problems and issues involving living beings.

**7**

**Author details**

Rafael Trindade Maia1

Cuité, Paraiba State, Brazil

Semiarid, Sumé, Paraiba State, Brazil

provided the original work is properly cited.

\* and Magnólia de Araújo Campos2

1 Federal University of Campina Grande, Center for Sustainable Development of

© 2021 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,

2 Federal University of Campina Grande, Center of Education and Health,

\*Address all correspondence to: rafael.rafatrin@gmail.com

*Introductory Chapter: Genetic Variation - The Source of Biological Diversity*

*DOI: http://dx.doi.org/10.5772/intechopen.96499*

*Introductory Chapter: Genetic Variation - The Source of Biological Diversity DOI: http://dx.doi.org/10.5772/intechopen.96499*
