4.4 Genetic diversity and adaptation

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

Explain the principles of natural selection in the evolution of populations

1. Mutation: Random gene mutations can result in [named] new alleles of a gene

2. Advantage: In certain [named] environments, the new allele might benefit its possessor [explain why] → organism has a selective advantage

3. Reproduction: Possessors are more likely to survive and have increased reproductive success

4. Inheritance: Advantageous allele is inherited by members of the next generation (offspring)

5. Allele frequency: Over many generations, [named] allele increases in frequency in the population

Name the 3 types of adaptations

• Anatomical

• Physiological

• Behavioural

Describe the Anatomical adaptation

Structural / physical features that increase chance of survival

Describe the Physiological adaptation

Processes / chemical reactions that increase chance of survival

Describe the Behavioural adaptation

Ways in which an organism acts that increase chance of survival

Name the 3 types of selection

• Directional Selection

• Stabilising Selection

• Disruptive Selection

Directional selection

• E.g. antibiotic resistance in bacteria

• Organisms with an extreme variation of a trait, e.g. bacteria with high level of resistance to a particular antibiotic

• Environment: Often a change, e.g. antibiotic introduced

• Increased frequency of organisms with alleles for extreme trait

• Normal distribution curve shifts towards extreme trait

Stabilising Selection

• E.g.Human birth weight

• Organisms with a modal variation of a trait e.g. babies with an average weight

• Environment: Usually stable

• Increased frequency of organisms with alleles for average trait

• Normal distribution curve similar, less variation around the mean

Disruptive Selection

• Favours extreme phenotypes at intermediate expense

• Important in bringing evolutionary change

• Caused by a change in environmental conditions (eg. Seasonal temp changes).

• Example: In an environmental with black and white rocks. White rabbit lives: camouflaged; Grey rabbit dies: seen by predator; Black rabbits lives:camouflaged