Evolution Flashcards
What is evolution?
The change over time in the proportion of individuals in a population differing in 1 or more inherited traits.
What happens during evolution?
Changes in allele frequency occur through the non-random process of genetic drift.
What does natural selection act on?
Genetic variation in populations
What does variation in traits in a population arise from?
Mutation.
What is mutation?
The original source of new sequences of DNA
What can the new sequences that come from mutations be?
Novel alleles
Most mutations are …
Harmful or neutral
In rare cases mutations may be?
Beneficial to the fitness of an individual.
Populations produce more offspring than the environment can support. Which individuals survive longer to produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generations?
Individuals with variations that are better suited to their environment.
Selection results in…
The non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles.
What is sexual selection?
The non-random process involving the selection of alleles that increase the individuals chances of mating and producing offspring.
What may sexual selection lead to?
Sexual dimorphism.
What can sexual selection be due to?
Male-male rivalry and female choice.
What is male to male rivalry?
Large size or weaponry increases access to females through conflict.
What is female choice?
Involves females assessing the fitness of males.
When does genetic drift occur?
When chance events cause unpredictable fluctuations in allele frequencies from one generation to the next.
When is genetic drift more important?
In small populations, as alleles more likely to be lost from gene pool.
When do population bottle necks occur?
When population size is reduced for at least 1 generation.
When does founder effect occur?
Through the isolation of afew members of a population from a larger population. The gene pool of the new population is not representative of that in the original gene pool.
Why is gene pool altered by genetic drift?
Because certain alleles may be underrepresented or overrepresented and allele frequencies change.
When selection pressures are strong…
Rate of evolution can be rapid.
What are selection pressures?
The environmental factors that influence which individuals in a population pass on their alleles.
Examples of biotic selection pressures?
Competition, predation, disease, parasitism
Examples of abiotic selection pressures?
Changes in temperature, light, humidity, pH and salinity
What does the HW principle state?
In the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over generations.
What are the conditions for maintaining the HW equillibrium?
- No natural selection
- Random mating, no mutation
- Large population size
- No gene flow (through migration, in or out)
What can the HW principle be used to determine?
Whether a change in allele frequency’s is occurring in a population over time. change suggests evolution is occurring.
Formula for HW principle?
p2 + 2pq + q2 = 1
p=
q=
p= frequency of dominant allele
q= frequency of recessive allele
p2 =
q2 =
p2 = frequency of homozygous dominant genotype
q2 = frequency of homozygous recessive genotype
2pq=
Frequency of heterozygous genotype
What is fitness an indication of?
an individuals ability to be successful at surviving and reproducing.
What is fitness a measure of?
The tendency of some organisms to produce more surviving offspring than competing members of the same species.
What does fitness refer to?
The contribution made to the gene pool of the next generation by individual genotypes.
What is absolute fitness?
The ratio between the frequency of individuals of a particular genotype after. selection to those before selection.
Formula for absolute fitness
Frequency of particular genotype before selection / Frequency of particular genotype after selection
What is relative fitness?
The ratio of the number of surviving offspring per individual of a particular genotype to the number of surviving offspring per individual of the most successful genotype.
Formula for relative fitness?
Number of surviving offspring per individual of a particular genotype / Number of surviving offspring per individual of the most successful genotype.
What is Co-evolution?
The process by which 2 or more species evolve in response to selection pressures imposed by each other
What does a change in traits of 1 species act as?
A selection pressure on the other species.
When is co evolution frequently seen?
In pair of species that have symbiotic interactions.
What is symbiosis?
Co-evolved intimate relationship between members of 2 different species
What can the impacts of these symbiotic relationships be for the individuals involved?
Positive, negative or neutral.
What is mutualism?
Both organisms in the interaction are interdependent on eachother for resources or other services. As both organisms gain from the relationship, the interaction is (+/+)
What is commensalism?
Only one of the organisms benefit (+/0)
What is parasitism?
The parasite benefits in terms of energy or nutrients and the host is harmed as a result of the loss of these resources (+/-)
What does the red queen hypothesis state?
In a co-evolutionary relationship, change in the traits of 1 species can act as a selection pressure on the other species.
What does the red queen hypothesis mean?
Species in these relationships must adapt to avoid extinction.
