Lecture 4 - Evidence for evolution Flashcards
Who tested Darwin’s postulates hypothesis?
Rosemary and Peter Grant
1976-1978
How did Rosemary and Peter Grant test Darwin’s first
and second postulate?
Off coast of Ecuador in the Galapagos islands
Finches show variation in beak length so all captured and measured
Variation to support: parents with small beaks have offspring with shallow beaks, parents with deep beaks tend to have offspring with deep beaks
Large genetic component - heritable component with beak length
How does Rosemary and Peter Grant’s experiment support Darwin’s third postulate about reproduction not being random?
Individuals that reproduce the most are those with the most favourable variations
Beak depth increased, deeper beaks can cracker harder seeds which is advantageous
How does Rosemary and Peter Grant’s experiment support Darwin’s second postulate about some variation being heritable?
Variation to support
Parents with small beaks have offspring with shallow beaks, parents with deep beaks tend to have offspring with deep beaks
Large genetic component to determine beak length
How does Rosemary and Peter Grant’s support Darwin’s first postulate about variety within species?
Medium ground finches showed variation in beak depth
How has genetic variation been shown in the Chernobyl nuclear disaster with frogs?
Melanin protects against ionising radiation
Brighter frogs in background radiation areas
Darker frogs in high radiation conditions
What is the conclusion about Darwin hypothesis and microevolution?
Populations adapt genetically to the environment
Microevolution by natural selection is a theory
What is genetic drift?
Changes in allele frequencies in a population
What percentage of genes are protein coding genes?
1.5%
Why are mutations not always acted upon?
As many are not in coding genes
(only 1.5% of protein coding genes in the genome)
Mutations from natural selection not acted upon
What are overall trends in natural selection and allele fixation?
Dominant: rapid rise as seen in both heterozygote and homozygote
Recessive: slower rise - only visible in homozygotes so fixation takes longer
How can genetic drift occur by sampling error?
Not every sperm contributes to next generation
Massive attrition occurs due to death
Sampling error is causing evolution to happen rapidly
How did Richard Lenski measure long term evolution?
E. Coli grown in medium with glucose and citric acid for carbon source
Sub-cultured every day for 30 years, every 75 days samples taken and frozen as fossil records
3 flasks developed mutations and some cells affected DNA repair mechanisms causing mutant streams
How did citrate used in aerobic conditions evolve in Lenski long term experiment?
Citric receptor only expressed in anaerobic conditions
In aerobic conditions transporter is not expressed so E.Coli cannot utilise external citrate as an energy source
Gene is duplicated by mutation causing strains being able to utilise citrate as well as glucose as energy sources
What is gene flow?
The movement of alleles between previously separate populations
How can alleles move by gene flow?
Migration of adults and subsequent mating
Movement of gametes and subsequent fertilisation
Alleles migrating from one area to another and finding mating success
What are the 3 main mechanisms to gene flow?
- Genetic drift removes genetic variation within demes - causes differentiation between demes
- Gene flow introduces new alleles into demes within a metapopulation - can cause genetic homogeneity between demes
- Selection and reproductive isolation
What is a deme?
A sub-population
What is a meta-population?
Overall population
What is a species (at eukaryotic level)?
A population of organisms that can potentially or actually interbreed, giving viable fertile offspring
How is each species defined?
Defined on looks and how they act
Not breeding behaviour
What is the argument about tree frogs and chromosomal duplication with species?
Instant speciation occurred when a treefrog failed to sort its 24 chromosomes during meiosis, generating a new species
Identical in size, shape and colour to original but has 48 chromosomes and a different mating call
Gene exchange has occurred
What is the example of the tube mosquito with species differentiation?
Mosquitos adapted to having mice as host
Originally eggs lay in open spaces, multiple genetic changes to host on mammals
Londoners hid in tubes during blitz and caused the plague
How is the ‘Big Bird Lineage’ an example of macroevolution?
Immigrant bird found female partner
2 of the hybrid offspring mated together to produce fertile offspring
