2.2 Evolution Flashcards
Evolution
The change over time in the proportion of individuals in a population differing in one or more inherited traits
The change over time in the proportion of individuals in a population differing in one or more inherited traits
Evolution
Mutation
Rare, random changes to genetic sequences which can be harmful, beneficial, or neutral
Rare, random changes to genetic sequences which can be harmful, beneficial, or neutral
Mutation
How do eukaryotes pass genetic material
Vertically
How is genetic material passed in prokaryotes
Horizontally
Symbiosis
- co-evolved intimate relationships between members of two different species where atleast one of the two benefits
- the impact can be positive, negative, or neutral for the individuals involved
- co-evolved intimate relationships between members of two different species where atleast one of the two benefits
- the impact can be positive, negative, or neutral for the individuals involved
Symbiosis
How can evolution happen
- the random process of genetic drift
- the non random processes of natural selection and sexual selection
What can happen through
- the random process of genetic drift
- the non random processes of natural selection and sexual selection
changes in allele frequency in evolution
What does natural selection depend on
- variation in inherited traits arises as a result of mutation
- mutations is the original source of new sequences of DNA that can result in new alleles
- natural selection acts on genetic variation in populations
Populations produce ____ offspring than the environment can support
More
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 gave them an advantage to the next generation
- selection results in the non random increase in the frequency of advantageous alleles and the non random decrease in the frequency of deleterious alleles
Deleterious
An allele which is likely to have a negative effect
Sexual selection
- the non random process involving the selection of alleles that increase the individual chances of mating, and producing offspring
- can lead to sexual dimorphism
- the non random process involving the selection of alleles that increase the individual chances of mating, and producing offspring
- can lead to sexual dimorphism, male male rivalry, and female choice
Sexual selection
Sexual dimorphism
A difference in characteristics beyond the sexual organs (male and females having different traits)
Male male rivalry
Male’s large size or weaponry increases the access to females through conflict
Male’s large size or weaponry increases the access to females through conflict
Male male rivalry
Female choice
If makes cannot control access to females, females will chose a male based on traits he displays that are considered to be high quality
Females assessing the fitness of males
Fitness
- an indication of an individual’s ability to be successful at both surviving and reproducing
- measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species
- the contribution made to the gene pool of the next generation by individual genotypes
- can be defined in absolute or relative terms
Genetic drift
- random process resulting in an increase or decrease in the frequency of inherited traits
- no input from selection pressures, it is purely chance. Natural disasters play a big part
- occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
- more important in small populations as alleles are more likely to be lost from the gene pool
Genetic drift and population size relationships
As the population size increases, the genetic drift decreases
Bottleneck effect
When a population size is reduced for at least one generation
Founder effect
- happens 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
- happens 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
Founder effect
Genetic drift and the gene pool
a gene pool is altered by genetic drift because certain alleles may be under represented or over represented and allele frequencies change
Relationship between strength of selection pressures and the rate of evolution
The stronger the selection pressures, the faster the rate of evolution
Selection pressures
- the environmental factors that influence which individuals in a population pass on their alleles
- can be abiotic (temperature, light, humidity, pH, salinity) or biotic (competition, predation, disease, parasitism)
- random process resulting in an increase or decrease in the frequency of inherited traits
- no input from selection pressures, it is purely chance. Natural disasters play a big part
- occurs when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
- more important in small populations as alleles are more likely to be lost from the gene pool
Genetic drift
Hardy-Weinberg principle
- in the absence of evolutionary influences, alleles and genotype frequencies in a population will remain constant over the generations
- conditions for maintaining the HW principle: no natural selection, random mating, no mutation, large populations as alleles size, no gene flow (through migration - in or out)
Hardy Weinberg equation
p + q = 1
p^2 + 2pq + q^2 = 1
p = frequency of dominant allele
q = frequency of recessive allele
p^2 = frequency of homozygous dominant gene type
2pq = frequency of heterozygous genotype
q^2 = frequency of homozygous recessive genotype
in a population that is in HW equilibrium, the frequency of the recessive allele for a particular trait is 0.7. what is the proportion of individuals heterozygous for this trait?
0.42
absolute fitness
- the ratio between the number of individuals of a particular genotype after selection to those before selection
- frequency of particular genotype after selection / frequency of particular genotype before selection
- if = 1, the frequency of that genotype is stable
- if >1, increase in frequency of genotype
- if <1, decrease in frequency of genotype
- the ratio between the number of individuals of a particular genotype after selection to those before selection
- frequency of particular genotype after selection / frequency of particular genotype before selection
absolute fitness
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
- number of surviving offspring of a particular genotype / number of surviving offspring per individual of the most successful genotype
co-evolution
- the process by which two or more species evolve in response to selection pressure imposed by each other
- a change in traits of one species acts as a selection pressure on the other species
- frequently seen in pairs of species that have symbiotic interactions
categories of co-evolution
- mutualism
- commensalism
- parasitism
mutualism
both organisms are interdependent on each other for resources or other services.
the interaction is + / +
both organisms are interdependent on each other for resources or other services.
the interaction is + / +
mutualism
commensalism
only one organism benefits
the interaction is + / 0
only one organism benefits
the interaction is + / 0
commensalism
parasitism
the parasites benefits in terms of energy or nutrients and the host is harmed as a result of the loss of these resources
the interaction is + / -
the parasites benefits in terms of energy or nutrients and the host is harmed as a result of the loss of these resources
the interaction is + / -
parasitism
coevolution example: pollinators and plants
- orchids have very exclusive relationships with their pollinators that has arisen through coevolution
- sometimes pollinators get a reward from the orchid, sometimes not
- orchids of the genus Ophrys often mimic female insects. the males attempt to mate with them and thus do the job of cross-pollinating plants
Co-evolution example: lions and zebras
- faster lions are more likely to catch food, and so survive and reproduce
- the faster zebras are able to escape the lions and so are more likely to survive and reproduce
- so, lions are exerting a selection pressure on the zebras and vice versa
- although both organisms are evolving, their relationship remains the same - this is true for all predator-prey relationships
co-evolution example: polar bears and seals
- the white coat of the polar makes it hard to spot against the snow, so they can sneak up on seals
- seal pups are also white, so they cant be seen by the polar bears
- the two species are exerting selection pressures on each other where being white gives a selective advantage
parasite
an organism which lives in or on another organism (its host) and benefits by deriving nutrients at the other’s expense
red queen principle
the host and parasite exert selection pressures on each other whereby:
- hosts that are better able to resist and tolerate parasitism have greater fitness
- parasites that are better able to feed, reproduce and find new hosts have greater fitness
- changes 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.
- both the parasite and host must evolve, and at a similar rate if their relationship is to remain unchanged and avoid extinction
Changes in the HW equation suggest what
Evolution is occurring
