StemUp: AQA A level Biology 3.4.4 Genetic diversity and adaptation

What is meant by genetic diversity? (1)

The number of different alleles present in a population

What is the importance of genetic diversity? (1)

A factor which enables natural selection to occur

Describe the principles of natural selection in the evolution of species (4)

1. Random mutation can result in new alleles of a gene

2. The new allele of a gene might benefit its possessor, leading to increased reproductive success

3. The advantageous allele is inherited by members of the next generation

4. As a result, over many generations the new allele increases in frequency in the population

When does directional selection occur? (3)

- When there is a change in an environment

- That favours one extreme phenotype over others

- Leading to a shift in the population's traits over time

What is an example of directional selection? (1)

Antibiotic resistance in bacteria

How do random mutations contribute to antibiotic resistance in bacteria? (1)

A few bacteria will possess an allele that provides resistance against a particular antibiotic

What role does antibiotic use play in the directional selection for bacteria? (2)

- Creates a selection pressure

- That favours bacteria with the antibiotic-resistant allele

How do antibiotic-resistant bacteria affect the population over time? (3)

- They survive and reproduce

- By binary fission

- Passing on the allele for antibiotic resistance to the next generation

What happens to non-resistant bacteria in the presence of antibiotics? (3)

- Most are killed

- Reproduce less frequently

- Leading to a decrease in their frequency in the population over generations

How does the frequency of antibiotic-resistant bacteria and the allele for antibiotic resistance change over generations? (2)

Increases in the population over generations

When does stabilising selection occur? (2)

- When the environment remains stable

- Selection favours organisms with phenotypes closest to the mean, or "norm"

What is an example of stabilising selection? (1)

Human birth weights

How does natural selection act in stabilising selection? (1)

Favours organisms with alleles for characteristics towards the middle of a trait range e.g. birth mass

What is the outcome for organisms with optimal birth mass alleles? (1)

Survive to breed and pass on their alleles to the next generation

How does stabilising selection affect allele frequency over generations? (1)

Frequency of alleles for optimal birth mass tends to remain stable over generations

What happens to babies with extreme birth mass alleles in stabilising selection? (2)

- Babies with alleles for very high or very low birth masses have a higher mortality rate

- Fewer survive to breed and pass on their alleles to the next generation

What are the different types of adaptations that arise from natural selection? (3)

- Anatomical

- Physiological

- Behavioural

What is an example of anatomical adaptations that arise from natural selection? (1)

Bigger beaks for eagles

What is an example of physiological adaptations that arise from natural selection? (2)

- Snakes and spiders produce venom to paralyse their prey

- Make them easier to digest

What is an example of behavioural adaptations that arise from natural selection? (2)

- Bears hibernate in the winter

- To conserve energy as there is less food in the winter