Conserved Sequences (HL) (HL IB Biology)

• A conserved sequence is a section of DNA or RNA that shows minimal mutations over time
  • A conserved sequence tends to be identical or similar across a species or a group of species
• Sequences that show little to no mutations over long periods of evolution are called highly conserved sequences
• Examples of such sequences include those that lead to DNA replication, transcription and translation, and proteins involved in cellular respiration
  • Sequences for DNA helicases, tRNA and ribosomes
  • Sequences for the respiratory proteins cytochrome c and ferredoxin 
• A number of hypotheses exist for the mechanisms that lead to conserved sequences and high conserved sequences
  • One is that the functional requirements of the gene are those that the organism cannot survive without
  • The other is that some sequences of DNA are subject to slower mutation rates

Functional requirements

• Conserved sequences and highly conserved sequences exist within genes that code for proteins that are essential for an organism's survival such as transcription and translation
• If these processes were unable to take place, due to mutations in the genes that code for essential proteins, then the cell would cease to survive
• Therefore the functional requirements of the cell maintain the conserved sequence and minimise mutations, as any mutations created would not be passed on to future generations
• We can hypothesise that natural selection maintains conserved sequences by necessity and and does not let any mutations pass to future generations

Slower mutation rates

• This hypothesis suggests that certain sections of gene sequences are less prone to mutations and the mutation rate is much slower than in other areas of the genome
  • Mutation rate is how many changes there is to the DNA sequence over time
  • It can be measured as
    • The number of base pair changes in a single gene at each generation or cell division
    • Or, the number of base pair changes in the whole genome per generation
  • DNA repair and proofreading mechanisms are very active in coding regions of the genome, and within genes that have high functionality
    • It is thought that areas where there are lower mutation rates do not have lower mutation but that they are spotted and corrected more frequently and so do not show up in sequenced DNA
  • Error correcting and proofreading is less active in areas of non-coding DNA so here higher rates of mutation are found