Module 6

• Charles Darwin, known as the Father of Evolutionary Biology, observed variation within populations and realized the importance of variation with respect to changes that take place in populations over time, allowing adaptation and evolution to take place
• Variation


  A product of recombination of traits from sexual reproduction
• Traits are not expressed at equal frequencies and there are underlying mechanisms that lead to such differences

  
• Gene


  The basic unit of inheritance that facilitates the transfer of traits from one generation to the next through the information stored in the DNA
• Allele


  Different or alternative forms of a gene
• Genotype


  The allelic combination an individual has
• Phenotype


  The trait expressed by the genotype
• Gene pool


  All the genes in every individual in a population at any given

  time; the available alleles present in the population
• Computing allelic and genotypic frequencies

  1. Identify individuals carrying the allele

  2. Sum the number of alleles

  3. Divide by total number of alleles to get frequency

  
• Hardy-Weinberg Equilibrium


  • Developed by Godfrey Hardy and Wilhelm Weinberg in 1908
  • Assumptions: large population, random mating, no migration, no mutation, no selection
  • Allelic frequencies do not change from one generation to the next
  • Genotypic frequencies are determined by the allelic frequencies

  
• Factors affecting population gene frequency over time

  • Migration (gene flow)
  • Mutation
  • Genetic drift (founder effect, bottleneck effect)
  • Natural selection
• In a population at Hardy-Weinberg equilibrium, the allelic frequencies can be determined once the genotypic frequencies are known

  
• In nature, populations are open and affected by factors like migration, mutation, genetic drift, and natural selection, which can change the genotypic and allelic frequencies
• Migration


  Also referred to as gene flow
• Mutations in a population


  • Cause change in genetic and allelic frequencies
  • Provided that mutated individuals will be fertile and produce viable offspring
• Genetic drift


  May cause complete elimination of some alleles by chance
• Genetic drift

  1. Founder effect

  2. Bottleneck effect
• Founder effect


  Accidental elimination of a certain allele may still occur in a population with random mating
• Bottleneck effect


  Occurs when a catastrophe happens e.g. forest fires, volcanic eruption
• Natural selection affects allelic and genotypic frequencies over time as the environment 'selects' traits will be favored in the population, depending on the advantage it poses to the individual, which we call its fitness value
• An allele that has a higher fitness value within an environmental context will make the individual that carries it have a greater chance of surviving and reproducing, which then increases the chance of that allele to be passed on to numerous offspring and several generations
• Through time, this selective reproductive success will lead to changes in the gene frequencies in the populations and a change in the frequency of traits expressed
• Eventually, there will be enough changes to arise for the population to diversify and lead to new species
• The basic unit of evolution is the population
• When variations within populations diverge enough, new species may arise
• Populations are the basic unit of evolution, which is defined as the change in gene frequencies over time
• Albinism is a condition where individuals have significantly reduced levels of melanin pigments in their tissues, most notably in the epidermis.
• Polydactyly is where afflicted individuals have extra fingers or toes.
• • homozygous dominant -FF
  • heterozygous dominant - Ff
  • homozygous recessive - ff
• In males, those that have at least one dominant allele (BB or Bb) will manifest baldness while those that are homozygous recessive (bb) will be normal. In the case of women, however, it takes two dominant alleles (BB) for the trait to manifest itself.