inheritance and evolution

• what are the two main types of variation?

  • continuous
  • discontinous
• describe the characteristics of continuous variation

  • normal distribution
  • quantitative
  • environment AND multiple genes influences phenotypic expression
  • wide range of variation with no distinct categories
  • polygenic (controlled by more than one gene)
  • each gene provides an additive component
  • different alleles at each gene locus have small effect on phenotype
  • different genes have combined effect
• describe the characteristics of discontinuous variation

  • qualitative differences between phenotypes
  • distinguishable categories
  • no intermediates
  • monogenic (only one gene involved)
  • if more than one gene is involved, it works in a epistatic way
  • different alleles at single gene locus have larger effects on phenotype
  • environmental factors have little influence
• is discontinuous variation affect by the environment?

  NO - determined purely by genetic factors
• what five assumptions does the Hardy Weinberg principle rely on?

  • no sexual selection - all genotypes have same reproductive success
  • no mutation
  • no gene flow- where an individual travels from one population and breeds with another, transferring alleles between the two populations
  • no genetic drift- random changes in allele frequencies- one allele in a small population (with low genetic biodiversity) has a greater impact than others and becomes more frequent, therefore by chance other alleles are lost in a population
  • no natural selection
• what are five factors that affect evolution?

  • mutation- formation of new alleles
  • sexual selection- increase of allele frequencies that allow reproductive success
  • natural selection- advantageous alleles in the gene pool increase in frequency
  • genetic drift- one organisms moves from one population to another and alleles are exchanged between the two populations, changes allele frequencies
  • gene flow- random changes in allele frequencies due to one allele having a greater impact than others and becoming more frequent in a small population- the others die out
• what are the problems of a small population size?

  • limited genetic diversity
  • less able to adapt
  • can be due to genetic bottlenecks: where few individuals within a population survive an event, reducing the gene pool. Only alleles available to be passed onto offspring are those of the survivors
• Population size is affected by limiting factors. What are these limiting factors?

  • density dependent factors- competition, population size etc- factors that are related to the size of the population
  • Density independent factors- factors that have nothing o do with the size of the population- climate, seasonal change
• what is the founder effect?

  extreme form of genetic drift- geographically isolated individuals form new colonies, smaller gene pool compared to original population, rare alleles have larger frequencies and impact
• state the three different types of selection

  • stabilising
  • directional
  • disruptive
• what are the factors of stabilising selection?

  • normal distribution
  • example of natural selection
  • normal characteristics are selected for (positive selection) and extremes are selected against (negative selection)
  • therefore increase in frequency of in average alleles and a reduction of the frequency of the alleles at the extremes
  • same alleles selected for in successive generations if environment remains stable
  • the two extremes are at either side of the graph, the norms are in the middle

  
• what are factors of directional selection?

  • change in the environment and the most common phenotype is no longer the most advantageous
  • organisms which have more extreme phenotypes are positively selected for
  • allele frequencies shift towards extreme phenotypes, evolution occurs

  
• what is speciation?

  the formation of new species through the process of evolution. Organisms belonging to the new species can no longer interbreed to produce fertile offspring with organisms of the original species
• explain the process of speciation

  • members of a population become isolated and cannot interbreed with the rest of the population as there's no gene flow
  • alleles within the groups undergo random mutations. The environments of each group may be different or change, so characteristics will be selected for and against due to different selection pressures
  • accumulations of mutations lead to large changes in phenotypes. Both populations cannot interbreed to produce fertile offspring and are reproductively isolated