biology - 2.2a - 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, what do 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?
Genetic variation in populations.
What does variation in traits arise as a result of?
Mutation.
What is mutation?
The original source of new sequences of DNA. These new sequences can be novel alleles.
What are most mutations?
Harmful or neutral, but in rare cases they may be beneficial to the fitness of an individual.
What can populations produce?
More offspring than the environment can support.
What do individuals with variations that are better suited to their environment tend to do?
Survive longer and produce more offspring, breeding to pass on those alleles that conferred an advantage to the next generation.
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.
What can sexual selection be due to?
Male-male rivalry and female choice.
What is male-male rivalry?
Large size or weaponry increases access to females through conflict.
What is female choice?
It 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.
Where is genetic drift more important?
In small populations, as alles are more likely to be lost from the gene pool.
What is important for genetic drift?
Bottleneck and founder
effects.
When do population bottlenecks occur?
When a population size is reduced for at least one generation.
How do founder effects occur?
Through the isolation of a 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.
What is a gene pool altered by?
Genetic drift because certain alleles may be underrepresented or over-represented and allele frequencies change.
When can the rate of evolution be rapid?
Where selection pressures are strong.
What are selection pressures?
The environmental factors that influence which individuals in a
population pass on their alleles.
What can selection pressures be?
Biotic: competition, predation, disease, parasitism;
Abiotic: changes in temperature, light, humidity, pH, salinity.
What does the Hardy-Weinberg (HW) principle state?
That, 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 and no gene flow (through migration, in or
out).
What can the HW principle be used to determine?
Whether a change in allele frequency is occurring in a population over time.
How do you use the HW principle to calculate allele, genotype and phenotype frequencies in populations?
p^2 + 2pq + q^2 = 1
Changes suggest evolution is occurring.
What is p?
Frequency of dominant allele.
What is q?
Frequency of recessive allele.
What is p^2?
Frequency of homozygous dominant genotype.
What is 2pq?
Frequency of heterozygous genotype.
What is q^2?
Frequency of homozygous recessive genotype.
