2.2 Evolution Flashcards
what is evoluiton
the change, over successive generations, in the proportion of individuals in a population differing in one or more inherited traits
what is natural selection
non-random process whereby certain alleles occur more frequently within a population because they confer a selective advantage
what is sexual selection
the non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring
what is genetic drift
the random change in how frequent a particular allele occurs within a small population
which evolutionary changes are random and which are non-random
natural selection - non-random
sexual selection - non-random
genetic drift - random
what is a mutation
rare, random changes to genetic sequences which can be harmful, neutral or, in rare cases, beneficial to the fitness of an individual
mutations are the original source of new sequences of DNA
variation in traits arise as a result of mutation
how do selection pressures arise
populations produce more offspring than the environment can support, resulting in selection pressures
individuals with variations that are better suited to the 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
the non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles
what can sexual selection lead to
sexual dimorphism
what is sexual dimorphism
physical difference between males and females of a species
sexual selection can be due to:
male-male rivalry
female choice
what is male-male rivalry
large size or weaponry increases access to females through conflict
what is female choice
involves females assessing the fitness of males
why is genetic drift more important in small populations
alleles are more likely to be lost from the gene pool
genetic drift occurs because of:
the bottleneck effect
the founder effect
what is the bottleneck effect
occurs when there is a disaster of some sort that reduced a population to a small handful, which rarely represents the actual genetic makeup of the initial population. this leaves smaller variation among the surviving individuals
what is the founder effect
the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population. the gene pool of the new population is not representative of that in the original gene pool
how is a gene pool altered by genetic drift
certain alleles may be under-represented or over-represented and allele frequencies change
when selection pressures are strong, the rate of evolution can be
rapid
what are selection pressures
the environmental factors that influence which individuals in a population pass on their alleles
selection pressures can be:
biotic or abiotic factors
examples of biotic factors
competition
predation
disease
parasistism
examples of abiotic factors
temperature light humidity pH salinity
what is the Hardy-Weinberg (HW) principle
in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations
conditions for maintaining the HW equilibrium are:
no natural selection random mating no mutation large population size no gene flow (through migration, in or out)
what can the HW principle determine
whether a change in allele frequency is occurring in a population over time
what does changes in the allele frequency suggest
evolution is occurring
what is the HW principle formula
p² + 2pq + q² = 1
what does p represent in the HW principle
frequency of dominant allele
what does q represent in the HW principle
frequency of recessive allele
what does p² represent in the HW principle
frequency of homozygous dominant genotype
what does 2pq represent in the HW principle
frequency of heterozygous genotype
what does q² represent in the HW principle
frequency of homozygous recessive genotyope
what is fitness
the indication of an individual’s ability to be successful at surviving and reproducing
what is fitness a measure of
tendency of some organisms to produce more surviving offspring that 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 types of fitness
absolute
relative
what is absolute fitness
the ratio of frequencies of a particular genotype from one generation to the next
what is the formula for absolute fitness
frequency of a particular genotype after selection
/
frequency of a particular genotype before selection
what does it mean if absolute fitness is 1
the frequency of that genotype is stable
what does it mean if absolute fitness is a value greater than 1
an increase in the genotype
what does it mean if absolute fitness is a value less than 1
a decrease in the genotype
what is relative fitness
the ration of surviving offspring of one genotype compared with other genotypes
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
where a change in the traits of one species acts as a selection pressure on another species with which it frequently interacts
co-evolution is frequently seen in
pairs of species that have symbiotic interactions
what is symbiosis
an interrelationship between members of two different species, whereby at least one species benefits
the impact of symbiotic relationships can be … for the individuals involved
positive (+)
negative (-)
neutral (0)
name the symbiotic interactions
mutualism
commensalism
parasitism
what is mutualism
both organisms in the interaction are interdependent on each other for resources or other services as both organisms benefit from each other (+/+)
what is commensalism
an interrelationship between organisms of two different species in which one species benefits and the other neither benefits nor suffers (+/0)
what is 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
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 theses relationships must adapt to avoid extinction
