Unit 2: Key Area 2 - Evolution Flashcards
What is evolution
Evolution is the change over time in the proportion of individuals in a population differing in one or more inherited traits
Describe the process of 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
What does natural selection act on and how does it arise
Natural selection acts on genetic variation in populations. Variation in traits arises as a result of mutation.
Describe how mutations give rise to genetic variation
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.
What happens during natural selection
During natural selection, the populations produce more offspring than the environment can support
Describe the process of natural selection
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
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.
Describe 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
What may sexual selection lead to
Sexual selection may lead to sexual dimorphism
What can sexual selection be a result of
Sexual selection can be due to male-male rivalry and female choice
Describe male to male rivalry
Male-male rivalry involves large size or weaponry. Increases access to females through conflict.
What is sexual dimorphism
Sexual dimorphism is when the male and female of a species look different
Describe female choice
Female choice involves females assessing the fitness of males.
When does genetic drift occur
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
When does population bottleneck occur
Population bottlenecks occur when a population size is reduced for at least one generation.
Describe the founder effects
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.
Why is the gene pool altered by genetic drift
A gene pool is altered by genetic drift because certain alleles may be underrepresented or over-represented and allele frequencies change
What happens when selection pressures are strong
Where selection pressures are strong, the rate of evolution can be rapid
What are selection pressures
Selection pressures are the environmental factors that influence which individuals in a population pass on their alleles.
Name the two types of selection pressures and give examples for each type
Biotic:
- competition
- predation
- disease
- parasitism
Abiotic: Changes in - temperature - light - humidity - pH - salinity
What does the Hardy - Weinberg (HW) principle state
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
What are the conditions for maintaining the HW equilibrium
The conditions for maintaining the HW equilibrium are: no natural selection, no random mating, no mutation, large population size and no gene flow (through migration, in or out).
What is the HW principle 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 is the HW principle used to calculate
Use the HW principle to calculate allele, genotype and phenotype frequencies in populations.
What does it mean if there is a change in allele frequency
If there is a change in allele frequency it suggests evolution is occurring
What is the formula for the calculation of the HW principle
p2 + 2pq + q2 = 1
What does p, q, p2, 2pq and q2 stand for
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
What is fitness an indication of
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
What can fitness be defined as
Fitness can be defined in absolute or relative terms
Describe absolute fitness
Absolute fitness is the ratio between the frequency of individuals of a particular genotype after selection, to those before selection
How to calculate absolute fitness
frequency of a particular genotype after selection
/ frequency of a particular genotype before selection
What does the value of absolute fitness mean if
a) it is 1
b) it is greater than 1
c) it is less than 1
a) If the absolute fitness is 1, then the frequency of that genotype is stable.
b) A value greater than 1 conveys an increase in the genotype
c) and a value less than 1 conveys a decrease in the genotype
Describe 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 to calculate 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
Co-evolution is the process by which two or more species evolve in response to selection pressures imposed by each other
What does the change in the trait of one species act like on other species
A change in the traits of one species acts as a selection pressure on the other species
Where is co evolution usually seen and what impacts do they usually have
Co-evolution is frequently seen in pairs of species that have symbiotic interactions
The impacts of these relationships can be positive (+), negative (-) or neutral (0) for the individuals involved
Describe 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 (+/+)
Describe Commensalism
Commensalism: only one of the organisms benefits (+/0)
Describe 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 and what does this mean
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
