Week 8 - Natural Selection Flashcards
What are the three possible theories for the history of life?
A) Evolution
B) Transformation
C) Separate Creation
How do you define evolution? (with example - Darwin’s Finches)
Evolution: A change in gene frequencies over time
States that:
- All species share a common ancestor
- Species have changed in a Darwinian sense of “descent with modification” (change in a population though time)
Darwin’s Finches - Descent by Modification
- Beak sizes and shapes - plant eaters and insect eaters adaptations
Define the following key themes: mutation, natural selection, genetic drift, founder effects
Mutation: the source of genetic variation
Natural Selection: the sifting of variation to produce adaptations
Genetic Drift: Random sampling of individuals over time (a drift in alleles)
Founder Effects: Small group of individuals ‘bud off’ or survive by chance
What are the three key ways to evidence evolution?
The fossil record
Observations of similarities and differences BETWEEN living species
Evolution in action - observing changes in real time
Fossil Record: What are intermediate forms? What does the order of fossils suggest?
Intermediate forms are present continuously in the fossil record. Shows an intermediate state between an ancestral trait and the current decendants
The order of fossils suggests evolutionary relationships (close fossils together, closer ancestrally)
What are living fossils?
Some species appear “unchanged” from when their evolutionary history began
Compare analogous vs homologous vs vestigial structures
Analogous: similar structures due to CONVERGENT EVOLUTION
Homologous: similar structures due to DESCENT WITH MODIFICATION
Vestigial: descent with modification - when features are no longer adaptative, but remains can often be seen in the skeleton
Phylogenetic Approaches: How do we build a phylogeny?
Genetic Material
Morphology (wings, legs, body colour)
- ISSUE: convergent evolution, and discriminating features
Changes in real time: what is microevolution?
Microevolution - evolution on a smaller scale (eg. Peppered moths during the industrial revolution)
What generates variation (3)?
- Random mutation
- Recombination (via sex)
- Gene flow
In the short term - recombination accounts for a great deal of genetic variation in wild populations
What is allele substitution?
Caused by natural selection and genetic drift - most populations are finite size and random fluctuations in allele frequencies can result in the replacement of alleles
Fixation and/or loss of alleles NOT due to selection = genetic drift
What effective population size?
The number of adult individuals in the population that actually reproduce
- genetic drift will proceed based on the effective population size
What are founder effects?
Loss of genetic variation that occurs when a new population is established by a very small number of individuals
Populations that go through a restricted size are said to have gone through a bottleneck
-> This can happen when new populations are founded
Gene flow: the process of genes moving from one population from another
- an example of this is GENETIC BOTTLENECK: drastic reduction in population –> next generation is representative of the surviving individuals
Natural Selection: outline the process?
A) Huge number of individuals are produced
B) Insufficient resources for all, so many die before reproducing
C) Individuals vary in attributes
D) Individuals with attributes better suited to the environment are less likely to die
E) These individuals will be over-represented in the next generation
What is sexual selection?
Competition for a share in reproduction
- Individuals differ in their reproductive output
- May depend on FECUNDITY - number of offspring they can produce
- May depend on attractiveness - number of mates they can attain and sum of their offspring
