Chapter 10: Population & Evolutionary Genetics Flashcards
Evolution
Change in allele frequency of a population
Charles Darwin
Origin of Species (1859)
Take a population (5,000 fruit flies)
Average survival without food (20 hours)
Starve until 80% of flies
Dies
Feed survivors, allow them to
Breed
Starve offspring until
80% dies, takes longer than parent generation (average survival without food: 23 hours)
Repeat for many generations, selecting for
Starvation survival, generation 60: average survival: 160 hours
How does evolution occur? How do allele frequencies change in population?
- Mutation
- Genetic drift
- Migration
- Natural selection
Mutation
Change to genome
Mutation are randome events, although they can be
Encouraged (mutagens)
Mutations are the root of all
Genetic variation
Most mutation have negative effect by the two following:
1) Generally create non-functioning genes
2) If mutation creates functional gene, may or may not make the organism more fit
Genetic drift
Random changes in allele frequency
Unlike natural selection, the change does not impact
Fitness directly; it is just which allele combination are inherited from parents
Genetic drift can cause traits to
Increase or decrease in a population and acts more strongly on small population
Genetic drift can lead to
Allele fixation: frequency of an allele = 100%
1) No variability
2) Genetic drift can lower variation
Genetic drift examples:
1) Founder effect
2) Bottlenecks
Founder effect
New, isolated populations exhibit different allele frequencies than original population
Bottlenecks
After large die off, survivors may have different allele frequencies than original population
Gene flow
Movement of individuals into other populations
Gene flow can introduce (or reintroduce) alleles to
Separated populations
Natural selection
Selection of traits (alleles) improving an organism chance of surviving and producing offspring (fitness)
Natural selection not directly removing
Unwanted genes
Natural selection origin of
Survival of the fittest
Natural selection requires 3 conditions
1) Variation in the trait
2) Heritability
3) Differential reproductive success
Three types of natural selection:
1) Stabilizing
2) Directional
3) Disruptive
Stabilizing
Favors the average/most common phenotype
Directional
Favors an extreme phenotype
Disruptive
Favors more than one phenotype
Sexual selection
Form of natural selection specifically acting on traits that increase the ability to gain mating opportunities
Sexual selection may
Decrease lifespan, but increase reproductive output
Sexual selection leads to
Sexual dimorphism
How do we get adaptations?
Populations typically have some variation in traits; all possible alleles form the gene fool
Adaptation key point:
The variation in phenotypes (dependent on the gene tool) is what natural selection acts upon
Different alleles:
Variation in phenotypes = adaptations
Genetic variation
1) Most populations exhibit genetic variability
2) No variation = no evolution
