6.1 genetics and evolution

• Mutations are changes in the sequence of nucleotides in DNA molecules
• Types of mutations include:

  • Insertion/deletion mutations where one or more nucleotide pairs are inserted or deleted from the sequence, causing a frameshift
  • Point mutation/substitution occurs where one base pair is replaced by another
  • Nonsense mutation stops translation early, giving rise to a truncated polypeptide
  • Missense mutation results in the production of a different amino acid, altering the tertiary structure of the protein
  • Silent mutation does not affect the amino acid sequence produced due to the degenerate nature of the genetic code
• Mutations can have neutral effects when they cause no change to the organism, or when a change in tertiary structure of the protein has no effect on the organism
• Some mutations are beneficial, such as humans developing trichromatic vision, while harmful mutations include those causing cystic fibrosis
• Gene expression can be controlled at the transcriptional, post-transcriptional, and post-translational levels
• Transcriptional control includes the lac operon in E.coli, where the concentration of glucose and lactose affects the transcription of structural genes
• Gene expression can also be controlled by transcription factors that switch genes on and off by interacting with the promoter sequence of DNA
• Post-transcriptional control involves editing the primary mRNA transcript to remove introns and create a mature transcript of exons
• Post-translational control includes the activation of proteins like adrenaline with cyclic AMP through a cascade of enzyme reactions
• Homeobox genes are involved in controlling the development of body plans of organisms by regulating transcription through binding to DNA
• Meiosis is a form of cell division that produces genetic variation through crossing over of chromatids and independent assortment of chromosomes
• Apoptosis is a form of programmed cell death that controls the number of cells and prevents cancer by breaking down cell contents and engulfing cell fragments
• Key terms include allele, locus, phenotype, genotype, dominant, recessive, homozygous, heterozygous, and codominance
• Linkage is when genes for different characteristics are located at different loci on the same chromosome and inherited together
• Monogenic inheritance involves a single gene controlling a phenotype, like cystic fibrosis
• Sex linkage depends on the gender of the individual, while autosomal linkage involves genes located on the same chromosome
• Epistasis is the interaction of different loci on the gene, with recessive and dominant epistasis affecting gene expression
• The chi squared test is a statistical test used for discontinuous variation data to determine if the null hypothesis is correct
• The Hardy-Weinberg Equation estimates allele frequencies in a population and checks for changes in allele frequency over time
• The niche of a species is its role within the environment, and natural selection is based on better adapted species surviving
• Species that share the same niche compete with each other, and the better adapted species survive
• Natural selection is the process in which fitter individuals who are better adapted to the environment survive and pass on advantageous alleles to future generations
• Organisms are adapted to their environment in various ways:

  • Anatomical adaptations are physical adaptations, either external or internal
  • Behavioural adaptations are changes in behavior that improve the organism's chance of survival
  • Physiological adaptations are processes inside an organism's body that increase its chance of survival
• Evolution is the process by which the frequency of alleles in a gene pool changes over time as a result of natural selection
• Factors that can affect the evolution of a species:

  • Genetic drift is a phenomenon where there is a small change in allele frequency
  • Genetic bottleneck is a rapid reduction in population size which affects genetic variation in future generations
  • Founder effect is a decrease in genetic diversity that occurs when the population descends from a small number of ancestors
• Speciation is the process by which new species arise after a population becomes separated and cannot interbreed

  • Allopatric speciation is caused by a physical barrier
  • Sympatric speciation is where new species evolve from a single ancestral species when inhabiting the same geographic region
• Artificial selection is the process where selection pressures are artificially created by humans, allowing the breeding of desired characteristics
• Principles of DNA sequencing:

  • DNA sequencing begins with mapping to identify the locus of a particular gene within the genome
  • Fragments of DNA are inserted into bacterial artificial chromosomes to form a genomic DNA library
  • The fragments are sequenced using chain-termination, a technique developed by Sanger
• Gene sequencing allows for genome-wide comparisons between individuals and between species

  • Comparing genomes between species helps determine evolutionary relationships
  • Gene sequencing has allowed for the prediction of amino acid sequences in polypeptides and the development of synthetic biology
• DNA profiling is a forensic technique used to identify individuals by characteristics of their DNA

  • Main techniques used in DNA profiling are PCR and gel electrophoresis
• Genetic engineering involves the use of restriction enzymes to cut DNA at specific base sequences

  • Isolated DNA fragments can be placed in plasmids to create recombinant DNA molecules
  • Gene therapy involves the insertion of a normal allele into target cells to replace a faulty allele
• Ethical considerations regarding genetic engineering include concerns about the potential effects on the environment and access to genetically modified seeds for poorer farmers