2.2a - Drift and Selection Flashcards
Evolution is…
the change over time in the proportion of individuals in a population differing in a population in one or more inherited traits
During evolution, changes in allele frequency occur through…
the non-random process of natural selection and sexual selection and the random process of genetic drift
Natural selection acts on…
genetic variation in populations
Variation in traits arise as a results of…
mutation
Mutation is…
the original source of new sequences of DNA
New sequences of DNA can be…
novel alleles
Most mutations are…
harmful or neutral
In rare cases mutations can be…
beneficial to the fitness of an individual
Populations produce more…
offspring than the environment can support
Individuals with variations that are better suited to their environment tend to…
survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation
Selection results in…
the non-random increase in the frequency of advantageous alleles and the non-random decrease in the frequency of deleterious alleles
Sexual selection is…
the non-random process involving the selection of alleles that increase the individual’s chances of mating and producing offspring
Sexual selection may lead to…
sexual dimorphism
Sexual selection can be due to…
male-male rivalry and female choice
Male-male rivalry
large size or weaponry increases access to females through conflict
Female choice
females assessing the fitness of males
Genetic drift occurs when…
chance events cause unpredictable fluctuations in allele frequencies from one generation to the next
Genetic drift is more important in…
small populations as alleles are more likely to be lost from the gene pool
Population bottlenecks occur when…
a population size is reduced for at least one generation
Founder effects occurs through…
the isolation of a few members of a population from a larger population
What happens if the surviving population is small after a population bottleneck/founder effect?
it may have lost a lot of its genetic variation and the allele frequencies might be different to the original population
The gene pool of the new population is not…
representative of that in the original gene pool
A gene pool is altered by…
genetic drift because certain alleles may be under-represented or over-represented and so the allele frequencies change
Where selection pressures are strong…
the rate of evolution can be rapid
Selection pressures are…
the environmental factors that influence which individuals in a population pass on their alleles
Biotic selection pressures
- competition
- predation
- disease
- parasitism
Abiotic selection pressures
changes in:
- temperature
- light
- salinity
- pH
- humidity
The Hardy-Weinburg (HW) principle states that…
in the absence of evolutionary influences, alleles and genotype frequencies in a population will remain constant over the generations
The 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)
The Hardy-Weinburg (HW) principle can be used to determine…
whether a change in allele frequency is occurring in a population over time
HW equation
P² + 2pq + q² = 1
p =
frequency of dominant allele
q =
frequency of the recessive allele
p² =
frequency of the homozygous dominant genotype
2pq =
frequency of the heterozygous genotype
q² =
frequency of the homozygous recessive genotype
Changes in allele frequency suggest…
evolution is occurring
