Evolution 2.2 Flashcards
what is evolution?
is the change over time in the proportion of individuals in a population differing in one or more inherited traits
what happens 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?
it acts on genetic variation in populations
what do populations produce?
more offspring than the environment can support
how are individuals with variation advantaged?
because they are better suited to their environment and tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation
what is sexual selection?
it 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 dimorphism
what can sexual selection be due to?
male-male rivalry and female choice
when can genetic drift occur?
when chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
why is genetic drift more important in small populations?
because alleles are more likely to be lost from the gene pool
what is the gene pool altered by and why?
it is altered by genetic drift because certain alleles may be under-represented or over-represented and allele frequencies change
what happens when selection pressures are strong?
the rate of evolution can be rapid
what does the Hardy-Weinberg (HW) principle state?
in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over the generations
what can the HW principle can be used to determine?
whether a change in allele frequency is occurring in a population over time
what does change suggest?
evolution is occurring
what is fitness an indication of?
an individual’s ability to be successful at surviving and reproducing
what does fitness refer to?
the contribution made to the gene pool of the next generation by individual genotypes
what can fitness can be defined in?
absolute or relative terms
what is absolute fitness?
the ratio between the frequency of individuals of a particular genotype after selection, to those before selection
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 co-evolution?
the process by which two or more species evolve in response to selection pressures imposed by each other
what is the bottleneck effect?
an example of genetic drift that can occur when a population size is reduced for at least one generation
what is the founders effect?
an example of genetic drift that occur through the isolation of a few members of a population from a larger population and the gene pool of the new population is not representative of that in the original gene pool
what are selection pressures?
environmental factors that influence which individuals in a population pass on their alleles
what can selection pressures be?
biotic
- competition
- predation
- disease
- parasitism
abiotic
- temperature
- light
- pH
- salinity
what are the conditions for maintaining the HW equilibrium?
- no natural selection
- random mating
- no mutation
- large population size
- no gene flow through migration, in or out
what is the HW equation and what does each symbol stand for?
p2 + 2pq + q2 = 1
p2 = frequency of homozygous dominant genotype
2pq = frequency of heterozygous genotype
q2 = frequency of homozygous recessive genotype
what happens if the absolute fitness is 1?
frequency of that genotype is stable
what happens if the absolute fitness has a value greater than 1?
conveys an increase in the genotype
what happens if the absolute fitness has a value less than 1?
conveys a decrease in the genotype
where is co-evolution frequently seen?
in pairs of species that have symbiotic relationships
what is symbiosis and what are the impacts of it?
co-evolved intimate relationship between members of two different species
the impacts can be positive (+), negative (-) or neutral (0) for the individual species involved
what is mutualism?
a symbiosis in which the species in the interaction are interdependent on each other for resources or other services and since both species gain the interaction is (+/+)
what is commensalism?
a symbiosis in which only one of the species substantially benefits and for the other the relationship is neither substantially positive or negative so it is neural (+/0)
what is parasitism?
a symbiosis in which the parasite species benefits in terms of energy or nutrients while the host species is harmed by the loss of resources (+/-)
what does the Red Queen Hypothesis state?
in a co-evolutionary relationship, change in the traits of one species can act as a selection pressure on the other species, which must adapt to avoid extinction
what is each species in a symbiosis relationship called?
a symbiont
