2.2.1 evolution: drift and selection Flashcards
what is evolution
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 processes of genetic drift
what does natural selection act on
the genetic variation in populations
how does variation in traits arise
mutation
what is mutation
the original source of new sequences of DNA. they can be novel alleles. most mutations are harmful or neutral
can mutations be beneficial to the fitness of an individual
yes
how much offspring do populations produce
more than the environment can support
which individuals tend to survive longer and produce more offspring, breeding to pass on alleles that confer an advantage to the next generation
individuals with variations that are better suited to their environment
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 is sexual selection
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, which is when the different sexes of a species have distinct differences in size or appearance
what can cause sexual selection
male-male rivalry and female choice
what is male male rivalry
large size or weaponry which increases access to females through conflict
what does female choice involve
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
what is the founder effect
this occurs through the isoltion of a few members of a population from a larger population. the gene pool of the new population is not as representative of that in the original gene pool
what are gene pools altered by
genetic drift
how are gene pools altered by genetic drift
because certain alleles may be under represented or over represented and allele frequencies changes
when can the rate of evolution be rapid
when selection pressures are strong
what are selection pressures
these are environmental factors that influence which individuals in a population pass on their alleles
what are examples of biotic selection pressures
competition
predation
disease
parasitism
what are examples of abiotic selection pressures
changes in temperature
light
humidity
pH
salinity
what does the HW principle state
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
what can the HW principle be used to determine
whether a change in allele frequency is occurring in a population over time
what is the HW principle
p2 + 2pq + q2 = 1
what does p mean in the HW principle
the frequency of the dominant allele
what does q mean in the HW principle
the frequency of the recessive allele
what does p2 mean in the HW principle
the frequency of the homozygous dominant genotype
what does 2pq mean in the HW principle
the frequnecy of the heterozygous genotype
what does q2 mean in the HW principle
the frequency of the homozygous recessive genotype
what do changes in allele frequency in a population over time suggest
that evolution is occuring
