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, resulting in a truncated polypeptide
  • Missense mutation changes a codon, producing a different amino acid and altering the tertiary structure of the protein
  • Silent mutation changes a codon but does not affect the amino acid sequence due to the degenerate nature of the genetic code
• Mutations can have neutral effects when they cause no change to the organism, occur in non-coding regions, or result in a change in tertiary structure that has no effect
• Some mutations are beneficial, like humans developing trichromatic vision, while harmful mutations include those leading to cystic fibrosis
• Gene expression can be controlled at the transcriptional, post-transcriptional, and post-translational levels
• Transcriptional control involves the lac operon in E.coli, where the presence of glucose and lactose affects the binding of the repressor to the operator region, regulating gene expression
• Transcription factors can 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 can activate proteins like adrenaline through cyclic AMP, starting a cascade of enzyme reactions
• Homeobox genes regulate the development of body plans by coding for transcription factors that switch genes on and off at specific developmental stages
• Apoptosis is programmed cell death that controls the development of body plans, ensuring a constant number of cells to prevent cancer
• Phenotypic variation includes discontinuous (e.g., blood type) and continuous (e.g., height) variations influenced by genetic and environmental factors
• Meiosis produces genetic variation through crossing over of chromatids and independent assortment of chromosomes, leading to the production of haploid gametes
• Key terms:

  • Allele: alternative form of a gene
  • Locus: specific position of a gene on a chromosome
  • Phenotype: observable characteristics of an organism influenced by genotype and environment
  • Genotype: alleles present within cells for a particular trait
  • Dominant: single allele required for expression
  • Recessive: characteristic expressed only in the absence of a dominant allele
  • Homozygous: two identical alleles
  • Heterozygous: two different alleles
  • Codominance: both alleles contribute to the phenotype
• Linkage is when genes for different characteristics are located 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 due to gene location on sex chromosomes, for example, haemophilia
• Epistasis involves the interaction of different gene loci, where one locus can mask or suppress the expression of another
• Chi-squared test is a statistical test used for discontinuous variation data to determine if the observed and expected results differ significantly
• Hardy-Weinberg Equation estimates allele frequencies in a population and checks for changes over time, with p representing the dominant allele frequency and q the recessive allele frequency
• The niche of a species is its role within the environment, and natural selection favors better-adapted species for survival
• 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
• 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: small change in allele frequency due to not all individuals reproducing, amplified in very small isolated groups
  • Genetic bottleneck: rapid reduction in population size affecting genetic variation in future generations, caused by natural disasters
  • Founder effect: decrease in genetic diversity 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: caused by a physical barrier, leading to reduced gene flow and different selection pressures
  • Sympatric speciation: new species evolve from a single ancestral species inhabiting the same geographic region, due to chromosomal errors during cell division leading to reproductive isolation
• Artificial selection is the process where selection pressures are artificially created by humans to breed desired characteristics

  • Example: dairy cow selection for high milk yields through hormone treatments and in vitro fertilization
  • Example: bread wheat: hexaploid with 42 chromosomes, a hybrid of three genomes AUAU, BB, and DD
• Principles of DNA sequencing:

  • Mapping to identify gene loci within the genome
  • Fragmenting DNA with restriction enzymes and inserting fragments into bacterial artificial chromosomes to form a genomic DNA library
  • Sequencing fragments with chain-termination technique developed by Sanger, based on selective incorporation of chain terminating nucleotides by DNA polymerase during replication
• Gene sequencing allows for genome-wide comparisons between individuals and species, aiding in determining evolutionary relationships and medical research

  • Predicting amino acid sequences in polypeptides and development of synthetic biology
• DNA profiling is a forensic technique to identify individuals by DNA characteristics and determine genetic relationships

  • Techniques: Polymerase chain reaction (PCR) for amplifying DNA, gel electrophoresis to separate DNA fragments by size
• Genetic engineering:

  • Restriction enzymes cut DNA at specific base sequences for gene transfer between species
  • Placing isolated DNA fragments in plasmids, creating recombinant DNA with DNA ligase
  • Using vectors like plasmids or viruses for gene transfer
• Gene therapy is the insertion of a normal allele into target cells to replace a faulty allele

  • Somatic gene therapy: introducing allele to target cells only, short-term solution
  • Germ line gene therapy: introducing allele to embryonic cells, permanent solution passed down to offspring
• Ethical considerations in genetic engineering:

  • Benefits include insect resistance in crops and genetically modified animals for pharmaceuticals
  • Concerns about environmental impact and accessibility of genetically modified seeds to poorer farmers