Key Area 2 - Evolution Flashcards
Drift & Selection
What is evolution?
Evolution is the change over time in the
proportion of individuals in a population
differing in one or more inherited traits.
What acts on genetic variation in populations?
Natural selection acts on genetic variation in populations.
What occurs during evolution?
During evolution, changes in allele frequency occur through the non-random processes of natural selection and sexual selection, and the random process of genetic drift.
How does variation arise in traits?
Variation in traits arises as a result of
mutation. Mutation is the original source of
new sequences of DNA. These new
sequences can be novel alleles. Most
mutations are harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual.
Explain sexual selection
Sexual selection is the non-random process
involving the selection of alleles that increase the individual’s chances of mating and producing offspring.
Populations produce more what that the environment connot support?
Populations produce more offspring than the environment can support.
What does selection result in?
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 tends to happen to individuals with variations that are better
suited to their environment?
Individuals with variations that are better
suited to their environment tend to survive
longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation.
Sexual selection may lead to what?
Sexual selection may lead to sexual
dimorphism.
What may sexual selection be due to?
Sexual selection can be due to male-male
rivalry and female choice.
Explain male-male rivalry and what female choice involves
Male-male rivalry: large size or weaponry
increases access to females through conflict.
Female choice involves females assessing
the fitness of males.
Explain how genetic drift occurs
Genetic drift occurs when chance events
cause unpredictable fluctuations in allele
frequencies from one generation to the next.
Why is genetic drift more important in small populations?
Genetic drift is more important in small
populations, as alleles are more likely to be
lost from the gene pool.
Explain the importance of bottleneck effects on genetic drift
Population bottlenecks occur when a
population size is reduced for at least one
generation.
Explain the importance of founder
effects on genetic drift
Founder effects occur through the isolation of a few 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.
What is a gene pool?
A gene pool is altered by genetic drift
because certain alleles may be underrepresented or over-represented and allele frequencies change.
Explain the relationship between selection pressures and the rate of evolution
Where selection pressures are strong, the
rate of evolution can be rapid.
Explain selection pressures
Selection pressures are the environmental
factors that influence which individuals in a
population pass on their alleles.
They can be biotic: competition, predation,
disease, parasitism; or abiotic: changes in
temperature, light, humidity, pH, salinity.
Explain what the Hardy-Weinberg (HW) principle states
The Hardy-Weinberg (HW) principle states
that, in the absence of evolutionary
influences, allele and genotype frequencies
in a population will remain constant over the generations.
List the conditions for maintaining the HW
equilibrium
The conditions for maintaining the HW
equilibrium are: no natural selection, random mating, no mutation, large population size and no gene flow (through migration, in or out).
What can the HW principle can be used to determine?
The HW principle can be used to determine
whether a change in allele frequency is
occurring in a population over time.
What can the HW principle be used to calculate?
Use the HW principle to calculate allele,
genotype and phenotype frequencies in
populations.
What is the HW principle formula?
p2 + 2pq + q2 = 1
p = frequency of dominant allele
q = frequency of recessive allele
p2 = frequency of homozygous dominant
genotype
2pq = frequency of heterozygous genotype
q2 = frequency of homozygous recessive
genotype
Fitness
What is fitness?
Fitness is an indication of an individual’s
ability to be successful at surviving and
reproducing.
What is fitness a measure of?
Fitness is 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?
It refers to the contribution made to the gene pool of the next generation by individual genotypes.
Name the two terms fitness can be defined as
Fitness can be defined in absolute or relative terms.
Explain absolute fitness
Absolute fitness is the ratio between the
frequency of individuals of a particular
genotype after selection, to those before
selection.
How do you calculate absolute fitness?
frequency of a particular genotype
after selection
____________________________________
frequency of a particular genotype
before selection
If the absolute fitness is 1, then the frequency of that genotype is stable. A value greater than 1 conveys an increase in the genotype and a value less than 1 conveys a decrease.
Explain relative fitness
Relative fitness is 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.
How do you calculate relative fitness?
number of surviving offspring per
individual of a particular genotype
_______________________________________
number of surviving offspring per
individual of the most successful genotype
Co-evolution
Explain co-evolution
Co-evolution is the process by which two or
more species evolve in response to selection pressures imposed by each other.
A change in the traits of one species acts as…
A change in the traits of one species acts as
a selection pressure on the other species.
Co-evolution is frequently seen in pairs of
species that have _______ interactions
Co-evolution is frequently seen in pairs of
species that have symbiotic interactions.
Explain symbiosis
Symbiosis: co-evolved intimate relationships between members of two different species.
What impacts of these relationships can happen for the individuals involved?
The impacts of these relationships can be
positive (+), negative (-) or neutral (0) for the individuals involved.
Name the three types of symbiotic interactions
Mutualism, commensalism, and parasitism
are types of symbiotic interactions.
Explain mutualism
Mutualism: both organisms in the interaction are interdependent on each other for resources or other services. As both organisms gain from the relationship, the interaction is (+/+).
Explain commensalism
Commensalism: only one of the organisms
benefits (+/0).
Explain parasitism
Parasitism: the parasite benefits in terms of
energy or nutrients and the host is harmed as the result of the loss of these resources (+/-).
What does the Red Queen hypothesis state?
The Red Queen hypothesis states that, in a
co-evolutionary relationship, change in the
traits of one species can act as a selection
pressure on the other species.
This means that species in these
relationships must adapt to avoid extinction.
