C1.7 - Applications of Evolution

Medical Application

Monitoring Mutations in Pathogens

• mutations in pathogens help predict and prevent disease outbreaks
• influenza virus mutates rapidly
• flu causes thousands of deaths each year
• scientists monitor flu strains yearly
• vaccines are made each year to match common strains
• a pandemic is a disease outbreak over a large area
• 2009 H1N1 was a global pandemic
• bubonic plague in 1340s killed one-third of Europe’s population
• no antibiotics existed during the plague

Alleles and Disease Resistance

• bacteria and viruses can mutate and become drug resistant
• some humans naturally resist certain infections
• 20% of Europeans carry D32 allele of CCR5 gene
• D32 allele helped resist past plagues and HIV
• D32 not found in African and Asian gene pools
• malaria increased sickle-cell allele in affected regions
• 1 in 25 Europeans carry cystic fibrosis allele
• 2 copies cause disease with early death
• 1 copy may give resistance to bacterial diseases like cholera and typhoid
• cholera was once widespread in Europe with high fatality
• survival advantage kept cystic fibrosis allele in gene pool

Influencing Disease Frequencies

• natural selection may not affect some disease alleles
• adult-onset diseases appear after reproduction
• Huntington’s disease starts in early to mid forties
• affected individuals may already have passed on the allele
• modern medicine can reduce or increase allele frequencies
• genetic testing can help people avoid passing on disease alleles
• treatments help people with diseases like cystic fibrosis live longer
• longer life allows reproduction and transmission of alleles

Evolution in Agriculture

Slowing Pesticide Resistance

• developing new pesticides is expensive and short-term
• refugia: local environments that have not been affected by regional ecological change
  • unsprayed areas in agricultural fields
• sprayed areas kill all but pesticide-resistant insects
• refugia allow both resistant and sensitive insects to survive
• interbreeding dilutes resistance if the allele is recessive
• fewer resistant offspring over generations
• keeps resistance levels low in the population
• reduces the need for new pesticide development
• similar approach used to slow antibiotic resistance in bacteria

Genetic Diversity in Crops

• crops are selected for specific traits
• farmers plant large numbers of the same variety
• Irish farmers relied only on the lumper potato
  • lumpers were clones with no genetic variation
  • low diversity increases vulnerability to disease
  • potato blight destroyed the entire crop in 1840s
  • 1 in 8 people died from starvation
• growing diverse varieties could have reduced impact
• single-variety planting still common today
• 1970 US corn crop hit by fungal infection
• 1980s grapevine pest (Phyllorexia vitifoliae) destroyed 800,000 hectares in California
• Cavendish banana is now at risk due to low diversity

Genetic Diversity in Livestock

• artificial selection reduces genetic diversity in livestock
• farm animals bred for specific traits over centuries
• creates genetically uniform breeds like white leghorn chickens
• white leghorns bred for egg production
• reduced diversity makes them vulnerable to disease
• outbreaks can wipe out entire populations
• increasing diversity requires breeding with other breeds
• modern tech like artificial insemination boosts desired traits
• semen from prized males can be frozen and shipped
• allows one male to father many offspring
• maintains traits but lowers genetic diversity within breed