Organisms and Evolution - Evolution Flashcards
Define evolution?
The change over time in the proportion of individuals in a population differing in one or more inherited traits
What occurs 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
Variations in traits arise as a result of what?
Mutation
What is mutation the original source of?
New sequences of DNA
What are the impact of mutations on organisms?
Most mutations are harmful or neutral, but in rare
cases they may be beneficial to the fitness of an individual
What does natural selection act on?
Genetic variation in populations
Why does natural selection occur?
Populations produce more offspring than the
environment can support
What happens in 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
Define sexual selection?
The non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring
What does sexual selection result in?
The non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles
What might sexual selection lead to?
Sexual dimorphism
What can be the cause of sexual selection?
Male-male rivalry and female choice
Define male-male rivalry?
Large size or weaponry increases access to females through conflict
Define female choice?
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
Where is genetic drift more important?
In small populations, as alleles are more likely to be lost from the gene pool
When do population bottle necks occur?
When a population size is reduced for at least one
generation
When do 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 altered by?
Genetic drift because certain alleles may be underrepresented or over-represented and allele frequencies change
When can the rate of evolution be rapid?
Where selection pressures are strong
Define selection pressures?
The environmental factors that influence which individuals in a population pass on their alleles
Selection pressures can be biotic or abiotic. Give examples?
Biotic:
competition, predation, disease and parasitism
Abiotic:
changes in temperature, light, humidity, pH, salinity
What does the Hardy-Weinberg principle state?
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 Hardy-Weinberg equilibrium?
No natural selection, random mating, no mutation, large population size and no gene flow (through migration, in or out)
What can the Hardy-Weingberg principle be used to determine?
Whether a change in allele frequency is occurring in a population over time
What is the Hardy-Weinberg 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
What is fitness?
An indication of an individual’s ability to be successful at surviving and reproducing
Define 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 are the two types of fitness?
Absolute and Relative
What is absolute fitness?
The ratio between the frequency of individuals of a particular genotype after selection, to those before
selection
What is the formula for absolute fitness?
Frequency of a particular genotype after selection / Frequency of a particular genotype before selection
What do the results of the absolute fitness formula show?
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
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
What is the 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 two or more species evolve in response to selection pressures imposed by each other
In co-evolution, a change in traits of one species acts as what on the other species?
A selection pressure
Where is co-evolution frequently seen?
In pairs of species that have symbiotic interactions
What is symbiosis?
Co-evolved intimate relationships between members of two different species
What can the impacts of symbiotic relationships be?
Positive (+), negative (-) or neutral (0) for the individuals involved
What are the three types of symbiotic interactions?
Mutualism, commensalism, and parasitism
Define 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 (+/+)
Define commensalism?
Only one of the organisms benefits (+/0)
Define 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 is the Red Queen Hypothesis?
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
