Evolution Flashcards
Define evolution:
Change in inherited characteristics of group of organism over time.
Occurs due to changes in frequency of different alleles in a population.
Define ‘population genetics’
Investigates how allele frequencies within a population changes over time.
Define gene pool.
Sum total of all genes in population at a given time.
Look at variation in different alleles of a single gene within gene pool.
What does the term ‘allele frequency’ refer to?
Relative frequency of a particular allele in the population.
Can change over time in response to changing conditions.
What does the Hardy-Weinberg principle state?
In a stable population with no disturbing factors, the allele frequencies will remain constant from 1 generation to the next and there will be no evolution.
p2 + 2pq +q= 1
What are the assumptions of the Hardy-Weinberg principle?
Large population size
Random mating
No mutations
No selection pressure –> no evolution.
What factors affect evolution?
Mutation –> leads to genetic variation
Sexual selection –> improve mating success by increasing sought out alleles
Gene flow
Genetic drift
Natural selection –> more characteristics that will improve chance of survival
What is the Hardy-Weinberg equation?
p2 + 2pq +q= 1
p + q = 1
p2 = frequency of homozygous dominant genotype in the
population
2pq = frequency of heterozygous genotype in the population
q2 = frequency of homozygous recessive genotype in the
population
Define the term ‘gene flow’
Movement of alleles between populations
Immigration/emigration results in changes of allele frequency of a population.
What is genetic drift?
Occurs in small populations
Change in allele frequency due to random nature of mutation
Appearance of new allele = greater impact in smaller populations
What is the impact of factors affecting evolution in small populations?
Limited genetic diversity
Cannot adapt to change as easily
More likely to become extinct
New strain of pathogen can wipe out whole population.
What are the 2 limiting factors that increase/decrease size of population?
Density dependent factors: depend on population size including competition, predation, parasitism
Density-independent factors: affect populations in same way –> climate change , human activities
What is genetic bottleneck?
Large reduction in population size which last for at least 1 generation.
Reduction in gene pool
+ genetic diversity
Positive bottleneck = beneficial mutation that has greater impact
Define term ‘founder effect’
Extreme example of genetic drift
Frequency of alleles that were rare in original (small) population, frequency of any alleles that were are will be much higher in new smaller population
Bigger impact during natural selection.
How does a normal distribution look like?
Distribution of different variants plotted
Bell shaped curve
What is stabilising selection?
Norm/average is selected (positive selection)
Extremes are selected against (negative selection)
Results in reduction in frequency of alleles at extremes
Increase in frequency of ‘average’ alleles.
What is directional selection?
Occurs wen there is change in environment and normal phenotype no longer most advantageous.
Organisms less common + extreme phenotypes positively selected
Allele frequency shifts towards extreme phenotypes –> evolution occurs
Describe disruptive selection
Extremes selected for
Norm selected against
e.g: Finch in Galapogas islands
