Preface

Population genetics is a fascinating branch of biology that focuses on the analysis of distribution and changes in the allelic frequencies of populations. Since its inception as a science in 1966, population genetics has advanced significantly due to the development of new molecular techniques, mathematical-statistical models, new software, and genomic databases. Currently, several theoretical and applied studies use the innumerable tools of population genetics for various inferences, analyzing the genetic structure of organisms for a better understanding of the dynamics of their populations.

This relatively recent science has important applications for the management of populations (natural and domesticated) as well as for evolutionary studies of the various factors that affect gene frequencies over time and across the world.

This book presents relevant results from carefully selected and evaluated population genetics studies and is presented in the form of chapters.

In the first chapter, the editors make a brief and objective presentation on population genetics, with an emphasis on the evolutionary processes that cause changes in the allelic and genotype frequencies in populations.

The second chapter deals with a study of the mapping of vigor genes in wine grapes as a quantitative (polygenic) inheritance, characteristics associated with the storage capacity of carbohydrates, and also the high metabolism and rapid development of these plants.

In the third chapter, the authors present a review addressing a series of genetic factors associated with the characteristics of interest for breeding one of the world's most important cultivars, rice.

The fourth chapter is about a study with AFLP markers applied to studies of populations of a fish species of commercial interest, with implications for adequate management of fish stocks, actions that aim to minimize inbreeding, and decrease of genetic diversity in these populations.

> **Rafael Trindade Maia** Federal University of Campina Grande, Sumé-PB, Cuité, PB, Brazil

> **Magnólia de Araújo Campos** Federal University of Campina Grande, Sumé-PB, Cuité, PB, Brazil

**1**

Section 1

Introduction

Section 1 Introduction

**3**

**Chapter 1**

**1. Introduction**

Introductory Chapter: Population

Genetics - The Evolution Process

*Rafael Trindade Maia and Magnólia de Araújo Campos*

Population genetics is defined as the sub-area of biology that studies the distribution and change in frequency of alleles. The population genetics is also the basis of evolution, and it has been established as a science; its main founders were JBS Haldane, Sir Ronald Fisher, and Sewall Wright. Since 1966, from the pioneering work of Fisher, Haldane, and Wright, the population genetics had accumulated a large mathematical theory, statistical tools, laboratory techniques, molecular markers, and huge information of polymorphisms in databanks [1]. The main concept in population genetics is focused on the Hardy-Weinberg theorem (also known as Hardy-Weinberg theorem or Hardy-Weinberg law). This central theorem preconizes that if the population size is large, with random mating, and mutation, selection, and migration are not significant, the allelic frequencies do not change over the generations. If not, the allelic and genotype frequencies will change from one generation to the next. These changes can affect directly in population's adaptive fitness, so information for applied studies and decisions can be provided by access-

Population genetics is an extremely useful tool for studies of microevolution, population dynamics, and conservation genetics. When accessing the genetic constitution of a population, several parameters can be conserved such as phenotypic frequencies, genotype frequencies, allelic frequencies, gene flow, heritability, genetic correlation, genetic diversity, heterozygosity, and several other indicators that allow an understanding of the genetic dynamics of the population in study. Through this information, it is possible to improve strategies for proper manage-

Among the evolutionary processes that interfere in the gene pool of populations,

altering their genetic constituent, they include mutation, migration (with gene

Mutation is the classic source of genetic variation, generating new alleles in a population. They direct the evolution and have different probabilities depending on the type of mutation, and this has implications for the evolution of genotypes. For example, if a G-A mutation occurs more frequently than A-G genotypes with the nucleotide A tend to be more common in the population. In summary, one can classify the mutations at synonymous and non-synonymous, that is, those that

as a Genetic Function

ing the genetic variation in populations.

**2. Evolutionary processes that interfere on genepool**

ment and control or even more efficient conservation actions.

flow), natural selection, and genetic drift [2].

## **Chapter 1**

## Introductory Chapter: Population Genetics - The Evolution Process as a Genetic Function

*Rafael Trindade Maia and Magnólia de Araújo Campos*

## **1. Introduction**

Population genetics is defined as the sub-area of biology that studies the distribution and change in frequency of alleles. The population genetics is also the basis of evolution, and it has been established as a science; its main founders were JBS Haldane, Sir Ronald Fisher, and Sewall Wright. Since 1966, from the pioneering work of Fisher, Haldane, and Wright, the population genetics had accumulated a large mathematical theory, statistical tools, laboratory techniques, molecular markers, and huge information of polymorphisms in databanks [1]. The main concept in population genetics is focused on the Hardy-Weinberg theorem (also known as Hardy-Weinberg theorem or Hardy-Weinberg law). This central theorem preconizes that if the population size is large, with random mating, and mutation, selection, and migration are not significant, the allelic frequencies do not change over the generations. If not, the allelic and genotype frequencies will change from one generation to the next. These changes can affect directly in population's adaptive fitness, so information for applied studies and decisions can be provided by accessing the genetic variation in populations.

### **2. Evolutionary processes that interfere on genepool**

Population genetics is an extremely useful tool for studies of microevolution, population dynamics, and conservation genetics. When accessing the genetic constitution of a population, several parameters can be conserved such as phenotypic frequencies, genotype frequencies, allelic frequencies, gene flow, heritability, genetic correlation, genetic diversity, heterozygosity, and several other indicators that allow an understanding of the genetic dynamics of the population in study. Through this information, it is possible to improve strategies for proper management and control or even more efficient conservation actions.

Among the evolutionary processes that interfere in the gene pool of populations, altering their genetic constituent, they include mutation, migration (with gene flow), natural selection, and genetic drift [2].

Mutation is the classic source of genetic variation, generating new alleles in a population. They direct the evolution and have different probabilities depending on the type of mutation, and this has implications for the evolution of genotypes. For example, if a G-A mutation occurs more frequently than A-G genotypes with the nucleotide A tend to be more common in the population. In summary, one can classify the mutations at synonymous and non-synonymous, that is, those that

entail changes in amino acid and those which do not cause changes in the peptide chain, also called neutral mutations. According to the theory proposed by Kimura neutrality, most mutations which attach the populations are of neutral type, since most non-synonymous mutations cause deleterious effects on the phenotypes of individuals [3].

Genetic drift is the change in gene frequency due to an event of random selection of individuals, usually in small populations (**Figure 1**). Genetic drift can have serious consequences for the population and can cause alleles to permanently disappear from a population, reducing their genetic variability. Drift can occur in two ways: the founder effect and bottleneck effect. The founder effect is the decrease of genetic diversity due to a new population established by few individuals [4, 5],

**5**

**Author details**

crops, and many other species.

provided the original work is properly cited.

Rafael Trindade Maia\* and Magnólia de Araújo Campos

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

Universidade Federal de campina Grande, Sumé-PB, Cuité, PB, Brazil

(deleterious mutations) tend to be eliminated (purified selection).

© 2019 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,

*Introductory Chapter: Population Genetics - The Evolution Process as a Genetic Function*

while bottleneck effect is the reduction of population size by environmental events

The impacts of genetic drift in a population will vary according to the effective

*Nf* + *Nm*

where *Ne* is the effective population, *Nm* is the number of breeding males, and *Nf*

Migration with reproductive success (**Figure 2**) allows the introduction of new alleles into the population, thus altering their genetic structure. Gene flow is one of the main parameters to evaluate the degree of structuring between populations of

Natural selection, a process observed by Charles Darwin, is the adaptation of organisms to the environment. It acts through the selection of genotypic changes in a given population. Through natural selection, mutations that increase the chances of individuals surviving and procreating tend to be preserved and multiplied in populations (positive selection), and mutations that decrease population fitness

The future of population genetics is very promising. The crucial progress in this field has showed that today, it is particularly relevant for the comprehension of genetic variation among populations from many species. Advances in population genetics will impact strongly the way we deal with biodiversity, pathogenic species,

(1)

(earthquakes, famines, floods, disease, fires, or droughts) [6].

*Ne* <sup>=</sup> <sup>4</sup>*NfNm* \_\_\_\_\_\_

is the number of breeding females.

*Migração com fluxo gênico. Source: Google images.*

the same species [7].

**Figure 2.**

population size (*Ne*), which can be estimated by the following equation:

*DOI: http://dx.doi.org/10.5772/intechopen.84418*

**Figure 1.** *Genetic drift. Source: Google images.*

*Introductory Chapter: Population Genetics - The Evolution Process as a Genetic Function DOI: http://dx.doi.org/10.5772/intechopen.84418*

**Figure 2.** *Migração com fluxo gênico. Source: Google images.*

*Integrated View of Population Genetics*

individuals [3].

entail changes in amino acid and those which do not cause changes in the peptide chain, also called neutral mutations. According to the theory proposed by Kimura neutrality, most mutations which attach the populations are of neutral type, since most non-synonymous mutations cause deleterious effects on the phenotypes of

Genetic drift is the change in gene frequency due to an event of random selection of individuals, usually in small populations (**Figure 1**). Genetic drift can have serious consequences for the population and can cause alleles to permanently disappear from a population, reducing their genetic variability. Drift can occur in two ways: the founder effect and bottleneck effect. The founder effect is the decrease of genetic diversity due to a new population established by few individuals [4, 5],

**4**

**Figure 1.**

*Genetic drift. Source: Google images.*

while bottleneck effect is the reduction of population size by environmental events (earthquakes, famines, floods, disease, fires, or droughts) [6].

The impacts of genetic drift in a population will vary according to the effective population size (*Ne*), which can be estimated by the following equation:

$$N\_c = \frac{4N\_f N\_m}{N\_f + N\_m} \tag{1}$$

where *Ne* is the effective population, *Nm* is the number of breeding males, and *Nf* is the number of breeding females.

Migration with reproductive success (**Figure 2**) allows the introduction of new alleles into the population, thus altering their genetic structure. Gene flow is one of the main parameters to evaluate the degree of structuring between populations of the same species [7].

Natural selection, a process observed by Charles Darwin, is the adaptation of organisms to the environment. It acts through the selection of genotypic changes in a given population. Through natural selection, mutations that increase the chances of individuals surviving and procreating tend to be preserved and multiplied in populations (positive selection), and mutations that decrease population fitness (deleterious mutations) tend to be eliminated (purified selection).

The future of population genetics is very promising. The crucial progress in this field has showed that today, it is particularly relevant for the comprehension of genetic variation among populations from many species. Advances in population genetics will impact strongly the way we deal with biodiversity, pathogenic species, crops, and many other species.

### **Author details**

Rafael Trindade Maia\* and Magnólia de Araújo Campos Universidade Federal de campina Grande, Sumé-PB, Cuité, PB, Brazil

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

© 2019 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.

## **References**

[1] Charolesworth B, Charles Worth D. Population genetics from 1966 to 2016. Heredity. 2017;**118**:s2-s9

[2] Kimura M. The Neutral Theory of Molecular Evolution. Cambridge: Cambridge University Press; 1983

[3] Gillespie JH. Population Genetics. A Concise Guide. Baltimore/London: The Johns Hopkins University Press; 1998. pp. 19-48. 169 páginas. ISBN: 0-8018-5755-4

[4] Provine WB. Ernst Mayr: Genetics and speciation. Genetics. 2004;**167**(3):1041-1046

[5] Templeton AR. The theory of speciation via the founder principle. Genetics. 1980;**94**(4):1011-1038

[6] William RC Jr. Bottleneck: Humanity's Impending Impasse. USA: Xlibris Corporation; 2009. pp. 290. ISBN: 978-1-4415-2241-2

[7] Frankham R, Briscoe DA, Ballou JD. Introduction to Conservation Genetics. Cambrige: Cambridge University Press; 2002. ISBN: 9780521639859

**7**

Section 2

Population and

Quantitative Genetics

Section 2
