3.4.4 - Genetic diversity and adaptation Flashcards
Topic 4
What is genetic diversity?
Number of different alleles of genes in a population
What are alleles and how do they arise?
● Variations of a particular gene (same locus) → different DNA base sequence
● Arise by mutation
What is a population?
● A group of organisms of the same species in a particular space at a particular time
● That can (potentially) interbreed (to produce fertile offspring)
Explain the importance of genetic diversity
● Enables natural selection to occur
● As in certain environments, a new allele of a gene might benefit its possessor
● By resulting in a change in the polypeptide (protein) coded for that positively changes its properties
● Giving possessor a selective advantage (increased chances of survival and reproductive success)
What is evolution?
● Change in allele frequency (how common an allele is) over many generations in a population
● Occurring through the process of natural selection
(1) and (2) are major factors in evolution and contribute to the diversity of living organisms
(1) Adaptation
(2) Selection
Explain the principles of natural selection in the evolution of populations
- Mutation
> Random gene mutations can result in [named] new alleles of a gene - Advantage
> In certain [named] environments, the new allele might benefit its possessor
[explain why] → organism has a selective advantage - Reproduction
> Possessors are more likely to survive and have increased reproductive success - Inheritance
> Advantageous allele is inherited by members of the next generation (offspring) - Allele frequency
> Over many generations, [named] allele increases in frequency in the population
Natural selection results in species that are better adapted to their environment:
Describe 3 types of adaptations
● Anatomical - structural / physical features that increase chance of survival
● Physiological - processes / chemical reactions that increase chance of survival
● Behavioural - ways in which an organism acts that increase chance of survival
Selection types
- Directional selection
= Selection favours individuals that vary in one direction away from the mean of the population - Stabilising selection
= Selection favours average individuals. It preserves the characteristics of a population
Explain how directional selection may occur
- If environmental conditions change, the pheonotypes that are best suited to new conditions are most likely to survive
> Often a change in selective pressures - Individuals with an extreme variation of trait (fall either left or right of mean) will possess a phenotype more suited to the new conditions
- These individuals are more likely to survive and reproduce
- So they contribute more offspring (and the alleles they possess) to the next generation than other individuals
- Overtime, mean will move in the direction of these individuals
> normal distribution curve shifts towards extreme trait.
> Directional selection results in phenotypes at one extreme of the population being selected for and those at other extreme being selected against
Example of directional selection
- Antibiotic resistance in bacteria
> the change in environment is the introduction of antibiotics
Explain how stabilising selection may occur
- If environmental conditions remain stable, it is the individuals with phenotypes closest to the means that are favoured.
- These individuals are more likely to pass their alleles on to the next generation
- Those individuals with phenotypes at the extremes are less likely to pass on their alleles
- Stabilising selection therefore tends to eliminate the phenotypes at extremes
- Organisms with an average variation of a trait have a selective advantage
> increased frequency of organisms with alleles for average trait
> normal distribution curve now has less variation around the mean
Example of stabilising selection
Human birth weight
