Natural and Artificial Selection - Natural and Artificial Selection Flashcards
what are the key steps in natural selection
- genetic variation
- selection pressure
- reproductive success
- repeated over many generations
describe genetic variation in natural selection
- random mutations cause different alleles of genes
- this causes intraspecific variation
- very occasionally new alleles may be beneficial
define selection pressures
environmental factors that confer greater chances of survival and hence reproduction for some members of a population and lower chances for others
give some examples of selection pressures
- predation
- food availability
- diseases
do different habitats have different selection pressures
yes
describe reproductive success in natural selection
- the organisms with the advantageous adaptations are most likely to survive and reproduce
- they pass on alleles that code for beneficial characteristics to their offspring
describe repeated over many generations in natural selection
- this process is repeated over many generations so the beneficial alleles become more frequent in the population
- therefore the proportion of the population possessing the advantageous characteristic increases
what is the effect of the use of pesticides
creates a selection pressure for those individuals with some form of resistance to the insecticide
how may resistance develop
- insects may be able to metabolise the insecticide
- target receptor proteins on the cell surface membrane may be modified
why may pesticide resistance cause infection rates to climb
many insect species carry diseases
how can pesticide resistance cause bioaccumulation
- pesticides become concentrated in the food chain
- large number survive the insecticide application but hold it in their bodies
- predators eat these insects and get a large dose
how can pesticide resistance cause crop loss
insects can cause a great deal of damage before insecticide resistance is recognised by farmers
how can pesticide resistance kill beneficial or benign insects
broader and stronger insecticides may need to be used
what does resistance require
the development of new pesticides, a costly exercise
give some potential problems of antibiotic resistance
- overuse and misuse of antibiotics
- eventually a strain will be resistant to all known antibiotics
- new drugs will have to be developed
Describe the general process of natural selection
- genetic variation caused by a random mutation
- leads to a new allele of a gene which confers beneficial characteristic
- something acts as a selection pressure
- those with the resistant allele have reproductive success and are more likely to survive and reproduce
- passing on the favourable alleles to their offspring, process repeats over many generations so allele frequency increases
Define the gene pool
All the alleles of all the genes present in a population of interbreeding organisms
When does stabilising selection occur
When the environment is stable
Describe stabilising selection
The same alleles are selected for in every successive generation and the gene pool of the population remains roughly the same
What is selected for and against in stabilising selection
- extremes of phenotypes are selected against
- intermediate phenotypes are selected for
When does directional selection occur
If the environment changes, so there is a change in the selection pressure on the population
Describe directional selection
It is an evolutionary force of natural selection
- one extreme will be selected against and the other will have a selective advantage
- over time the allele frequency shifts towards an extreme
what is genetic drift
random fluctuations can occur in allele frequency within a population - purely by chance
where is genetic drift most likely
small populations
