KA 2: evolution: drift and selection Flashcards
what is evolution?
the change over time in the proportion of individuals in a population differing in one or more inherited traits
during evolution, when do changes in allele frequency occur?
-non-random processes of natural selection and sexual selection
-random process of genetic drift
what does natural selection act on in populations?
genetic variation
variation in traits arises as a result of…
mutation
what is mutation?
the original source of new sequences of DNA
what can the new sequences from a mutation be?
novel alleles
what are most mutations?
harmful or neutral
in rare cases they may be beneficial to the fitness of an individual
populations produce…
more offspring than the environment can support
what happens to individuals with variations that are better suited to their environment?
they tend to survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation
what does the selection result in?
the non-random increase in the frequency of advantages alleles and the non-random decrease in the frequency of deleterious alleles
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 does sexual selection lead to?
dimorphism
what can sexual selection 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
when does 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?
as alleles are more likely to be lost from the gene pool
when do population bottlenecks occur?
when a population size is reduced for at least one generation
when does the founder effect occur?
through the isolation of 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
why is a gene pool altered by genetic drift?
because certain alleles may be under-represented or over-represented and allele frequencies change
where 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: (give examples)
-biotic (competition, predation, disease, parasitism)
-abiotic (changes in temp, light, humidity, pH, salinity)
State The Hardy-Weinberg (HW) principle
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 HW equilibrium?
-no natural selection
-random mating
-no mutation
-large population size
-no gene flow (through migration, in or out)
what can the HW principle be used to determine?
whether a change in allele frequency is occuring in a population over time
what is the HW formula?
p2 + 2pq + q2 = 1
what does each letter in the Hardy-Weinberg (HW) formula mean?
p=frequency of dominant allele
q=frequency of recessive allele
p^2=frequency of homoxygous dominant genotype
2pq= frequency of heterozygous genotype
q^2=frequency of homozygous recessive genotype
changes suggest…
evolution is occuring
