Evolution Flashcards
Evolution
The 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 process of genetic drift
Natural selection
Acts on genetic variation in populations.
How does genetic variation come about?
Arises as a result of mutation.mutation is the original source of new sequences of DNA, these new sequences can be novel alleles
Process of natural selection
Populations produce more offspring than the environment can support, individuals with variations that are better suited to their environment tend to survive lager and produce more offspring, breeding to pass on their alleles that conferred on 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.
Sexual selection
The non-random process involving the selection of alleles that increase the individual’s chance of mating and producing offspring
What may sexual selection lead to?
Sexual dimorphism
What can be factors affecting sexual selection?
Male-male rivalry, female choice
Male-male rivalry
Large size or weaponry increases access to females through conflict.
Female choice
Involves females assessing fitness of males
Genetic drift
Occurs 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.
Population bottle necks
Occur when a population size is reduced for at least one generation.
Founder effects
Occur through the isolation of a few members ofa population from a larger population.the gene pool of the new population is not representative of that in the original gene pool
How is a gene pool altered by genetic drift?
Certain alleles may be under-represented or over-represented and allele frequencies change.
Selection pressures
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, pH, salinity
Hardy-weinberg principle
States that in the absence of evolutionary influences, allele and genotype frequencies in a population will remain constant over Te generations.
Conditions for maintaining hw principle
No natural selection, random mating, no mutations, large population size, no gene flow (through migration, in or out)
How con we use the hw principle?
To determine whether a change in allele frequency is occurring in a population over time
Fitness
An indication of an individual’s ability to be successful at surviving and reproducing, it is a measure of the tendency of some organisms to produce more surviving offspring than competing members of the same species.
What does fitness refer to?
The contribution made to the gene pool of the next generation by individual genotypes
