2.2 Flashcards
What is evolution?
change over time in the proportion of individuals in a population differing in 1+ inherited traits
How do changes in allele frequency occur?
in non-random processes (natural/sexual selection) and the random process of genetic drift
Describe genetic drift..
- random process
- occurs due to chance events (disease, predation, abiotic)
- more important in small populations, alleles more likely to be lost from gene pool
- masked in large populations due to number of individuals
What is the bottleneck effect of genetic drift?
when population size is reduced for at least one generation
chance event occurs, few random individuals survive.
population grows again over time but no same allele percentages present as before
variety in population can decrease and allele proportion change completely
What is the founder effect of genetic drift?
through isolation of few random individuals, the gene pool of new population is not representative of original gene pool
What can genetic drift result in?
due to random nature of allele fluctuation over time, can result in genetic variation reduction, having negative effect on ability to evolve, some alleles lost from a population and some retained
What happens when selection pressure are strong?
evolution rate can be rapid in these populations
What are selection pressure?
environmental factors which influence which individuals pass their alleles
Name biotic selection pressures…
- competition
- predation
- disease
- parasitism
Name abiotic selection pressures…
- temperature changes
- light
- pH
- humidity
- salinity
What is natural selection?
a non-random process in frequency of DNA sequences that increase survival (advantageous alleles) and non-random reduction in deleterious DNA sequences, certain genes selected as they code for proteins which form desirable characteristics
How do mutations work in natural selection
-acts upon genetic variation in populations
- trait variations arise as result of mutation
- mutation is the original source of new DNA sequences
- most mutations are harmful or neutral, but in rare cases they may be beneficial to fitness of an individual
How are individuals with advantageous alleles selected?
Populations produce more offspring than environment can support.
Individuals with variations better suited to environment survive longer and produce more offspring so advantageous alleles passed to next generation
What is sexual selection?
non-random process involving allele selection that increase individuals chance of mating and producing offspring
How does sexual selection work?
- operates through members of species having mating advantages
- trait selection solely concerned with increasing mating success
What may sexual selection lead to?
sexual dimorphism, male-male rivalry and female choice
What is sexual dimortphism?
where two sexes of the same species exhibit different characteristics beyond sexual organs
What is male-male rivalry?
large size, weaponry increase access to females to conflict
What is female choice?
females assess males fitness
What is the Hardy-Weinberg principle?
states that in absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over generations
What are conditions for maintaining the Hardy-Weinberg equilibrium?
- no natural selection
- random mating
- no mutation
- large population size
- no gene flow
What is the Hardy-Weinberg formula?
p² + 2pq + q² = 1, p + q = 1
p = frequency of dominant allele
q = frequency of recessive allele
p² = frequency of homozygous dominant genotype
2pq = frequency of heterozygous dominant genotype
q² = frequency of homozygous reccessive genotype
What is fitness?
an indication of an individuals ability to be successful at surviving and reproducing
refers to contribution made to gene pool of the next gen by individual genotypes
can be absolute or relative
How does environment affect fitness?
Overall fitness affected by environment, the fitness of phenotype/genotype will differ in different environments
What is absolute fitness?
the ratio between the number of individuals of a particular genotype after selection to those before
State absolute fitness formula…
genotype frequency after selection divided by genotype frequency before selection
What do results of absolute fitness formula mean?
If absolute fitness is 1 then frequency of genotype is stable.
If > 1 it conveys decrease
If < 1 it conveys increase
What is relative fitness?
the ratio of number of surviving offspring per individual of a genotype to number of offspring per individual of most successful genotype
State relative fitness formula…
surviving offpsring of genotype divided by surviving offspring of most successful genotype
How is reproductive success of an individual measured?
absolute fitness divided by average fitness
What is coevolution?
process in which 2+ species evolve in response to selection pressures imposed by each other
Name examples of coevolution…
- herbivores and plants
- pollinators and plants
- predators and prey
- parasites and hosts
What impacts can symbiotic relationships have?
+, - or 0
What are selection pressures in coevolution?
a change in traits in one species acts as selection pressure on other species
Describe the relationship between parasites and their hosts…
a parasitic relationship is one in which one organism (parasite) lives off of another organism (host) harming it and possibly causing death
How do some hosts have better fitness?
hosts better able to resist and tolerate parasites have greater fitness
How do some parasites have better fitness?
parasites better able to feed, reproduce and find new hosts have greater fitness
What is symbiosis?
the co-evolved intimate relationships between members of two different species
What types of symbiotic relationships are there?
- mutualism
- commensalism
- parasitism
Describe mutualism…
- interactions of both organisms are interdependant
- rely on each other for resource
- both organisms gain (+/+)
Describe commensalism…
- only one organism benefits
- (+/0)
Describe parasitism…
- parasite benefits in terms of energy or nutrients
- host is harmed as result of resource loss
- (+/-)
What is the Red Queen hypothesis?
states that, in a co-evolutionary relationship, change in the traits of one species act as selection pressures on the other species
species in these relationships must adapt to avoid extinction
How does Red Queen hypothesis effect parasitic relationship?
as a host evolves to deter parasites, the parasites will adapt to be able to continue to survive in their host
