Evolution Chapter 9.1 Flashcards
What is a gene pool?
All the alleles of all the genes of all individuals in the population
What is allele frequency?
The number of copies of a particular allele compared to the total number of alleles in a population’s gene pool
What leads to evolution within a population/microevolution?
The changing percentages or frequencies of alleles within populations
What are the common factors that lead to evolutionary change?
- Mutation
- Natural Selection
- Non-random mating
- Gene flow (migration)
- Genetic drift
(MNNGG)
How do mutations lead to evolutionary change?
- Random introduction of new alleles into gene pool
- Changes allele frequencies
Ex: anti-biotic resistance in bacteria
How does gene flow lead to evolutionary change?
- Movement of alleles from one population to another due to migration and interbreeding
- May change allele frequencies in either or both populations
What is non-random mating?
Mating among individuals on the basis of mate selection for a particular phenotype or due to inbreeding
What are the two types of non-random mating?
- Preferred phenotypes
2. Inbreeding
How does preferred phenotype relate to non-random mating?
- Mates chosen based on physical and behavioral traits (phenotype)
- Mates with desirable trait will pass down phenotype to offspring
What is sexual selection?
- Competition for female from males (fighting, displays)
What is sexual dimorphism?
Significant physical distinctions between sexes
What is inbreeding?
Closely related individuals breed together
How does inbreeding and non-random mating relate?
- Increases the frequency of homozygous genotypes
Negative effects: - Homozygous genotypes are common between close relatives and harmful recessive alleles are more likely to be expressed
What is genetic drift?
Random change in allele frequencies due to chance events in a breeding population
What is the difference between sample size and population size?
- Population size can greatly affect the gene pool of a population (less likely that parent gene will be reflected in next generation) - vice versa for large population size
- Smaller sample size, greater uncertainty
What are the two significant genetic drifts and what leads to them?
- Bottleneck Effect
- Founder Effect
Population size and sample size
What is the bottleneck effect?
- Population changes size quickly (reduced) because of natural happenings (disaster, disease)
- Survivors had an allele that only a fraction of the population had before the disaster and gene pool is loses diversity
- Survivors carry some, but not all, of original alleles
What is the founder effect?
- Change change in gene pool when a few individuals (“founders”) start a new, isolated population
- Founders carry some but not all alleles of original population
What are the three modes of natural selection?
- Stabilizing selection
- Directional selection
- Disruptive selection
(SDD)
What is stabilizing selection?
- Favours middle phenotype over extremes
- Reduces variance
- Graph: vertically stretched from original graph
Ex: Middle colour clams are able to survive than the extreme light/dark clams because they are easy to be spotted by predators
What is directional selection?
- Favours one extreme phenotype over other extreme phenotype
- Changes mean value of trait under selection
- Graph: shifted units to the right
Ex: Oyster shell thickness
What is disruptive selection?
- Favours extreme phenotypes over intermediate phenotypes
- Increases variance
- Population is divided into two distinct groups
- Graph: Two lumps
Ex: Middle coloured clams are not able to survive but the extreme light/dark are able to survive
What type of selection leads to the formation of new species?
Diversifying selection
