2f- Drift and selection Flashcards
What is meant by the term “evolution”?
The change over time in the proportion of individuals in a population differing in one or more inherited traits
During evolution, how 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
How does variation in traits arise?
As a result of mutation
What is the only source of new sequences of DNA?
Mutation
What effect do most mutations have on an individual?
Most are harmful or neutral, but in rare cases they may be beneficial to the fitness of the individual
How many offspring does a population produce?
More than the environment can support
What does natural 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 individuals tend to survive longer and produce more offspring and why?
Those with variations that are better suited to their environment, they then pass on those alleles that confer an advantage to the next generation
What is sexual selection?
The non-random process that involves the selection of alleles that increase the individuals chances of mating and producing offspring
What may sexual selection lead to?
Sexual dimorphism
What two things can sexual selection be due to (describe them)?
- male-male rivalry= large size or weaponry increases access to females through
conflict - 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
In what kind of populations does genetic drift have a bigger impact and why?
In small populations, as alleles are more likely to be lost from the gene pool
What are two examples of genetic drift?
- population bottleneck
- 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
Why is a gene pool altered by genetic drift?
Because certain alleles may be under-represented or over-represented and allele frequencies change
What can happen when 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
What are four examples of biotic selection pressures?
- competition
- predation
- disease
- parasitism
What are five examples of abiotic selection pressures?
- 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 five conditions for maintaining 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 occurring in a population over time
What do changes in the HW equilibrium suggest?
Evolution is occurring
