Topic 7

• Sex-linkage:

  • Color blindness caused by a recessive allele on the X chromosome
  • Question: Probability of children being color-blind when a non-color blind male reproduces with a female carrier
• Multiple alleles:

  • Example with blood groups
  • Question: Probability of parents with blood group AB and O having an offspring with blood group A
• Epistasis:

  • One gene influences the expression of another gene
  • Examples: coat color in mice, Labradors, and fruit color of vegetables
• Autosomal linkage:

  • Alleles linked on the same chromosome inherited together
  • In a dihybrid cross, gametes expected: RY or ry
• Crossing over in meiosis:

  • Results in new combinations of alleles in gametes
  • Observed results may differ from expected due to crossing over
• Hardy-Weinberg principle:

  • Mathematical model predicting allele frequencies within a population
  • Assumes no change in allele frequency between generations
  • Example question: Proportion of carriers for cystic fibrosis in the UK
• Key points:

  • Inheritance links to genetic diseases, DNA structure, natural selection, types of selection, and crossing over in meiosis
  • Predicting inheritance outcomes links to the chi-squared statistic
• Natural selection can lead to speciation
• Disruptive selection can ultimately lead to speciation
• Stabilising selection decreases the range of alleles and most individuals have the modal trait
• Directional selection changes allele frequency and makes one extreme trait's alleles more frequent
• Genetic and environmental factors contribute to a wide range of phenotypic variation within a population
• Primary sources of genetic variation are mutations, meiosis, and random fusion of gametes
• Predation, disease, and competition result in selection pressures
• Organisms with phenotypes giving them a selective advantage are more likely to survive and reproduce
• Differential reproductive success leads to changes in allele frequencies within a gene pool
• Speciation is the process that results in the creation of new species
• Reproductive isolation leads to the accumulation of differences in gene pools, making interbreeding impossible
• Allopatric speciation occurs due to geographical barriers separating populations
• Sympatric speciation occurs due to differences in reproductive behavior within a population
• Genetic drift is the change in allele frequency within a population between generations
• The smaller the population, the bigger the impact allele frequency changes have proportionally
• Three types of selection are stabilising, disruptive, and directional
• Mutations accumulate over many generations, leading to reproductively isolated populations with different DNA unable to interbreed
• Natural selection and evolution are linked to inheritance and the importance of DNA
• Sympatric speciation is linked to courtship behavior
• Speciation is linked to mutations
• Abiotic factors and biotic factors (interspecific and intraspecific competition) affect population size in ecosystems
• Adaptations develop through natural selection over many generations based on abiotic factors within ecosystems
• Biotic factors involve interactions between living components of an ecosystem, such as competition and predation
• Interspecific competition is competition between different species for limited resources
• Intraspecific competition is competition between the same species for resources and mates
• Competition for a mate links to courtship rituals
• Sampling techniques, such as using quadrats, are used to estimate population sizes in ecosystems
• Random sampling and representative sampling are important to avoid bias in estimating population sizes
• Different sampling methods, like belt transects and interrupted belt transects, can be used to estimate population sizes accurately
• Belt transect:

  • Quadrat is placed at every position along a tape measure
  • Sometimes more appropriate than random sampling with a gridded area
  • Used in ecosystems that are not uniform, such as a rocky shore
• Interrupted belt transect:

  • Quadrat is placed at uniform intervals along a tape measure, e.g., every 5 metres
• To ensure data for each area, the quadrat can be placed at intervals along the transect to measure the impact of changes in the environment
• Estimating population size:

  • Methods used to record species present: Density, Frequency, Percentage cover