Genetic Analysis Introduction

• Population Genetics


  Studies genetic composition of biological populations and the changes in genetic composition that result from various influences
• Types of Population Genetics

  • Theoretical Population Genetics
  • Experimental Population Genetics
  • Empirical population genetics
• Theoretical Population Genetics


  • Uses mathematical and computational models to understand the effects of different processes
• Experimental Population Genetics


  • Uses controlled laboratory and field experiments to test theoretical predictions
• Empirical population genetics


  • Studies genetic variation in natural populations often to understand population biology
• Population genetics is bound to the study of evolution and natural selection

  Evolution can be defined as any change in a population's genetic composition
• Natural selection is an important factor that can lead to changes in a population's genetic composition
• What population genetics is used to study

  • Evolutionary history
  • Genetic diversity
  • Ecology and Population Biology
  • Mating Systems
  • Forensics
  • Genetic Architecture of Trait Variation
• Genetic Architecture of Trait Variation


  • How many genes
  • Occurrence of genes
  • How many genes are inherited?
• The 4 processes that regulate changes in gene frequency

  • Genetic drift
  • Natural selection
  • Migration
  • Mutations
• Genetic drift


  Some alleles are not passed to the next generation by chance
• Natural selection


  Only some individuals with certain traits survive
• Migration


  New allele can enter a population
• Mutations


  • The source of new genetic variation
  • Generate new alleles
  • Change the number and frequency of alleles
• Evolution by chance is more common in smaller populations
• The concept belief was that species change and that relatives share similar traits
• The first concept of natural selection was written by a Muslim Biologist in 900AD
• From the 10th century to the 16th century, western culture believed in the great chain of being
• Discoveries in paleontology and geology led biologists to understand slow processes can occur over long periods
• Charles Darwin's two main ideas

  • Modern species were descended from common ancestors
  • The process of natural selection was the major mechanism of evolutionary change
• Darwin failed to provide a mechanism of inheritance, so people still believed in the blending theory
• The basis of evolution according to Darwin


  • More individuals are born than survive
  • Individuals vary
  • Some variations are inherited
  • Survival and reproduction are not random
• Traits are variable


  A trait that gives individuals fitness becomes abundant in the future generation
• When the heritable variation is related to survival and reproduction, evolution occurs
• The accumulation of advantageous variation allows a population to diverge over time
• Mendel's work was rediscovered in 1900 and showed that inheritance was due to the passing on of discrete hereditary units
• Saltionists thought that Mendel's work supported their view of evolution through discrete steps
• Gradualists found that Mendel's work was inconsistent with their observations of continuous traits and the process of radial evolution
• Hardy-Weinberg Principle


  Allele frequencies and genotype frequencies will remain constant in the absence of other factors
• The Hardy-Weinberg Principle changed the idea that dominant alleles would increase in frequency and take over populations
• R.A. Fisher's contributions


  • Variation in quantitative characters could be explained by Mendelian Inheritance
  • Developed important statistical techniques and developed quantitative genetics
  • Merged Mendel's and Darwin's ideas
  • Found that a continuous trait can be controlled by many genes through Mendelian inheritance
• J.B.S. Haldane's contributions

  • Developed the mathematical theory of natural selection and pioneered mathematical predictions of the changes in gene frequency
• Sewall Wright's contributions


  • Known for his work on inbreeding and effective population size
  • Emphasized evolution through genetic drift in small population
  • Discover the Shifting Balance Theory
• Shifting Balance Theory


  Describes evolution as a process by which favourable gene combinations come together in small isolated populations and then increase in frequency by selection
• Theodosius Dobzhansky's contributions


  • Used empirical data from natural and experimental Drosophila to support the theoretical work for Fisher, Wright and Haldane
  • Argued that mutation is the source of all variation
  • Initiated the Modern synthesis of evolutionary biology and genetics
• Lewontin & Hubby & Haris published the technique of protein electrophoresis in 1966, which revealed more genetic variation in natural populations
• Kimura's Neutral Theory of Molecular Evolution


  Most variation at the protein level is neutral, and variation is maintained by a balance between mutation and genetic drift
• Tomoko Ohta's Nearly Neutral Theory

  New mutations are slightly deleterious rather than completely neutral, and variation is maintained by a balance between mutation, genetic drift and selection
• From the 1980s to now, advancements in molecular genetics techniques have allowed for more detailed examination of past evolutionary events using analysis of whole genome sequences
• Gradualists 


  Believe that selection acts on small individual variation & therefore evolution is slow and gradual