The aim of population genetics is to model the dynamics of evolutionary change within and between populations i.e. a group of individuals who exist together in time and space and are capable of interbreeding. In human DNA approximately 0.08% of the nucleotide base pairs varies among individuals and thus populations genetics has been trying to establish why this is so. Four basic evolutionary forces responsible for genetic diversity in populations have been identified: mutation, natural selection, genetic drift and gene flow. Mutations are copying errors during DNA replication and transcriptions, which introduce new alleles into the population. Natural selection is the differential transmission of alleles into the next generation due to the consequences of functional differences on an individual’s survival and reproductive success. Genetic drift is the differential transmission of alleles into the next generation as a result of random sampling and has the greatest potential impact in small populations. Gene flow spreads alleles from one population into another via migration, making them more genetically similar to each other, and countering genetic differentiation by drift. I am going to examine the contribution of genetic drift, gene flow and natural selection to the levels of diversity and composition of genetic polymorphisms in different human populations. Further I am going to examine why some populations have greater diversity than others and compare the patterns of genetic diversity of humans and chimpanzees.
Table of Contents
1. POPULATIONS GENETICS OF HUMANS
Research Objectives and Themes
The primary aim of this work is to examine how the fundamental evolutionary forces of genetic drift, gene flow, and natural selection shape the genetic diversity and composition of polymorphisms within and between human populations. It further explores the reasons for varying levels of diversity across populations and compares these patterns between humans and chimpanzees.
- Mechanisms of genetic drift and its impact on allele frequencies.
- The influence of migration and gene flow on genetic homogenisation.
- Models of natural selection in diploid organisms.
- The neutral theory of molecular evolution.
- Comparative analysis of genetic diversity in humans versus chimpanzees.
Excerpt from the Book
Genetic drift
Genetic drift is a process through which gene frequency changes (over generations) are produced as a result of the finite number of individuals present in a population, and such changes are intrinsically random; i.e. non-systematic. Random genetic drift was introduced to population genetics through the work of Sewall Wright. He believed that the random properties of allele frequency change were important not only in understanding the exact changes from one generation to the next, but also in the way dif allowed evolution to proceed in novel directions which might otherwise be opposed by direct selection. The change in allele frequency due to genetic drift, while unpredictable in individual populations, on average causes populations to change in a predictable way. Drift on average causes there to be fewer alleles within populations, and variable allele frequencies over time. Two immediate consequences of drift effects are: (1) a gradual decay of within-population variation, ultimately leading to either fixation or loss of specific alleles and (2) genetic differentiation between populations can be created by genetic drift alone.
Summary of Chapters
1. POPULATIONS GENETICS OF HUMANS: This chapter introduces the core concepts of population genetics and analyzes how evolutionary forces like drift, migration, and selection dictate the levels and distribution of human genetic diversity compared to other species.
Keywords
Population genetics, genetic drift, natural selection, gene flow, allele frequency, mutation, neutral theory, polymorphisms, effective population size, evolutionary dynamics, genetic diversity, human evolution, chimpanzee genetics, diploid model, population bottleneck.
Frequently Asked Questions
What is the fundamental focus of this work?
The work focuses on modeling the dynamics of evolutionary change within and between human populations, specifically evaluating how basic evolutionary forces drive genetic variation.
What are the central themes discussed in the text?
The central themes include the mechanics of genetic drift, the homogenizing effects of gene flow, the modeling of natural selection, and the application of the neutral theory to understand molecular evolution.
What is the primary objective of the author?
The primary objective is to determine the contribution of genetic drift, gene flow, and natural selection to the levels of genetic polymorphisms and to explain why genetic diversity varies between human populations and chimpanzees.
Which scientific methods or models are highlighted?
The text highlights the 'standard' diploid model for selection, the 'island model' for gene migration, and the concept of 'effective population size' (Ne) to quantify evolutionary processes.
What is covered in the main body of the work?
The main body covers the theoretical mechanisms of drift, the role of migration in preventing subpopulation divergence, the outcomes of selection in diploid organisms, and the implications of the neutral theory regarding molecular polymorphism.
How are the key terms defined for this study?
The study utilizes terms such as genetic drift, gene flow, natural selection, and neutral theory to describe the specific ways in which allele frequencies change over generations and influence population structure.
How does the author explain the difference between human and chimpanzee genetic diversity?
The author attributes the higher variation in chimpanzees to a larger effective population size and a lack of gene flow between their geographically isolated subgroups, in contrast to humans.
What does the text conclude about the definition of human races?
The text suggests that based on genetic marker distributions, where 90% of variation occurs within local populations, the human species cannot be scientifically divided into distinct subspecies or subgroups.
- Quote paper
- BA (Oxon), Dip Psych (Open) Christine Langhoff (Author), 2002, Populations Genetics of Humans, Munich, GRIN Verlag, https://www.grin.com/document/14018
