4.4 Genetic diversity and adaptation

What is the definition of genetic diversity within a population?

The number of different alleles of genes present in the gene pool of a population.

What are alleles?

Different versions/variations of the same gene, found at the same locus on a chromosome.

How do new alleles arise?

They arise by mutation (a change in the DNA base sequence of a gene).

What is the biological definition of a population?

A group of organisms of the same species that live in the same area at the same time and can potentially interbreed to produce fertile offspring.

What is the primary evolutionary importance of genetic diversity?

It is the raw material that enables natural selection to occur.

How does a new allele lead to a potential advantage in a specific environment?

The new allele may result in the production of a polypeptide/protein with slightly different properties.

What is the benefit of having a protein with advantageous properties?

It may give the organism a selective advantage – an increased chance of survival and reproductive success in that particular environment.

What is the definition of evolution at the population level?

A change in the frequency of alleles within a population's gene pool over many generations.

Through what primary process does this change in allele frequency (evolution) occur?

Through the process of natural selection.

What is the first, random event that provides the variation for natural selection? (Mutation)

A random gene mutation occurs, producing a new allele of a gene.

Under what condition does this new allele become advantageous? (Advantage)

In a specific, named environment, the new allele confers a beneficial trait (e.g., disease resistance, better camouflage). This gives the organism a selective advantage.

What is the consequence of having a selective advantage? (Reproduction)

Organisms with the advantageous allele are more likely to survive to reproductive age and have greater reproductive success (produce more offspring).

What happens to the advantageous allele in the next generation? (Inheritance)

Because the possessors reproduce more, the advantageous allele is passed on (inherited) to a larger proportion of the next generation.

What is the long-term, population-level result of this process over many generations? (Allele Frequency)

The frequency of the advantageous allele increases in the population, while less beneficial alleles may decrease. This is evolution by natural selection.

What process leads to the development of adaptations in a species?

Natural selection.

What is the definition of an anatomical adaptation? Provide an example.

A structural or physical feature of an organism that increases its chance of survival.

• Example: Thick fur, streamlined body shape, camouflaged colouration.

What is the definition of a physiological adaptation? Provide an example.

A process or internal chemical/biochemical function that increases an organism's chance of survival.

• Example: Ability to produce antifreeze proteins, venom production, efficient water conservation in kidneys.

What is the definition of a behavioural adaptation? Provide an example.

A way in which an organism acts or responds that increases its chance of survival.

• Example: Migration, hibernation, mating rituals, playing dead.

Name the two main types of selection discussed.

Directional selection and Stabilising selection.

What is a classic example of directional selection?

The evolution of antibiotic resistance in bacteria.

Which individuals have the selective advantage in directional selection?

Individuals with an extreme variation of a trait (e.g., bacteria with a very high level of resistance to a specific antibiotic).

What type of environmental condition typically drives directional selection?

A changing environment or the introduction of a new selective pressure (e.g., introduction of an antibiotic, climate change).

What is the effect on the population's trait distribution over many generations?

The mean/average value of the trait shifts towards the advantageous extreme. The normal distribution curve moves (shifts) in one direction.

What is the effect on allele frequencies?

The frequency of alleles coding for the extreme trait increases in the population.

What is a classic example of stabilising selection?

The selection for average human birth weight.

Which individuals have the selective advantage in stabilising selection?

Individuals with the average/modal (middle) variation of a trait (e.g., babies of average weight).

What type of environmental condition is associated with stabilising selection?

A stable, unchanging environment where the current average trait is already optimal.

What is the effect on the population's trait distribution over many generations?

The mean/average stays the same, but the variation around the mean decreases. The distribution curve becomes narrower and taller.

What is the effect on allele frequencies?

The frequency of alleles coding for the average trait increases, while alleles for extreme traits decrease. Genetic diversity at that locus is reduced.