Genetic diversity and adaptation Flashcards
What is an allele?
- variety of a gene (recessive or dominant allele)
What is genetic diversity?
- the number of different alleles of genes in a population
What does genetic diversity enable?
- natural selection to occur
What is a gene pool?
- All the alleles, of all the genes, of all individuals in a population at a given time
What is natural selection?
- process where selection pressure (e.g predation, competition for food) acts on a population which in turn remove certain alleles from a population
What does genetic diversity allow/why is it important?
- Organisms are able to adapt to change in the environment
- Allows natural selection to occur
What is genetic diversity in a population increased by?
- Random mutations
- Gene flow - different alleles being introduced into a population when individuals from another
population migrate into it and reproduce
What at the three types of selection?
- Stabilising selection
- Directional selection
- Disruptive selection
Define stabilising selection
- modal traits has the selective advantage, occurs when there is no change in the environment
What does stabilising selection result in?
- overall reduction in the phenotype variation
- standard deviation decreases as individuals with the extreme trait decrease
- modal trait remains same
Give an example of stabilising selection
- human birth weights
Define directional selection
- one of the extremes has the selective advantage, occurs when there is a change in the environment
What does directional selection result in?
- one aspect of trait is emphasised as only one extreme is removed, other extreme has selective advantage
- modal trait changes
Give an example of directional selection
- Darwin’s finches in the Galápagos Islands
- antibiotic resistance in bacteria
Define disruptive selection
- favours extreme of a trait with selection against intermediate traits
What does disruptive selection result in?
- balanced polymorphism in the population and may lead to speciation
Give an example of disruptive selection
- grasses growing in tailing ponds of mines
What is evolution?
- change in allele frequency over many generations in a population
What does natural selection lead to?
- evolution
What does natural selection result in?
- species becoming better adapted to their environment
What can adaptations be categorised into?
- Anatomical
- Physiological
- Behavioural
Describe the process of natural selection
- New alleles for a gene are created by random mutations
- If new alleles increases the chances of the individual to survive in that environment, then they are more likely to survive and reproduce
- This reproduction passes on the advantageous allele to the next generation
- As a result, over many generations, the new alleles increases increases in frequency in the population
Describe how antibiotic resistance occurs
- A random mutation (change in the base sequence of DNA) occurs that allows the mutated bacteria to break down antibiotics (penicillinase)
- This gives mutated bacteria a selective advantage against the non mutated bacteria
- The non mutated bacteria is removed by selection pressure whilst the mutated bacteria survives and reproduces by binary fission, passing on the advantageous alleles in the presence of penicillin
- As a result, advantageous alleles increase
