Define 'Allele Frequency'.

Allele frequency is a measure of how common a specific allele is relative to other alleles for the same gene within a population's gene pool.

What is the difference between intraspecific and interspecific variation?

Intraspecific variation refers to differences between individuals of the same species (e.g., different hair colors in humans). Interspecific variation refers to differences between individuals of different species (e.g., the differences between a lion and a tiger).

How does the source of genetic variation differ from the source of environmental variation?

Genetic variation is caused by internal factors like mutations and the shuffling of alleles during sexual reproduction. Environmental variation is caused by external factors such as diet, lifestyle, or physical accidents that do not change the DNA sequence.

What is the distinction between a mutation and an adaptation?

A mutation is a random change in DNA that occurs in an individual. An adaptation is a characteristic that has become common in a population because it provides a survival advantage, resulting from the process of natural selection over many generations.

Why is it incorrect to say that an individual 'evolves' to survive a new predator?

Evolution is a change in allele frequencies within a population over time, not a change in a single individual. An individual either possesses the advantageous alleles to survive or it does not; it cannot change its own genetics in response to a threat.

What is the misconception regarding the 'purpose' of mutations?

The misconception is that mutations occur 'to help' an organism survive. In reality, mutations are random and spontaneous; they occur regardless of whether they will be beneficial, harmful, or neutral to the organism.

Why can't acquired traits, like a tan or a scar, contribute to evolution?

Acquired traits do not change the DNA sequence in the gametes (sperm or eggs). Only genetic information stored in the gametes can be passed to the next generation to influence the population's gene pool.

A gene pool is the complete set of all unique alleles present in a specific population of a species at a given time.

What is a 'Mutation'?

A mutation is a rare and random change in the sequence of DNA bases in a gene or a chromosome, which can lead to the creation of new alleles.

How does a mutation in DNA lead to a change in phenotype?

A mutation changes the DNA base sequence, which alters the mRNA transcript and the resulting amino acid sequence. This change in amino acids can alter the protein's shape and function, which manifests as a different physical or biochemical trait (phenotype).

Genetic Variation Within a Population | OCR GCSE Science

Combined Science A Gateway / Biology

Genes, Inheritance & Selection

Genetic Variation Within a Population

Summary

Genetic variation refers to the diversity of alleles and genotypes within a single population of a species. This variation is the fundamental requirement for evolution, as it provides the raw material upon which natural selection acts, allowing populations to adapt to changing environments over time.

1. Definition & Core Concepts

Intraspecific Variation: This term describes the differences in characteristics between individuals of the same species. These differences can be physical (phenotypic), such as height or color, or biochemical, such as blood type.
Alleles: These are alternative versions of a specific gene that arise through mutation. The combination of alleles an individual possesses (genotype) determines their observable traits (phenotype).
Gene Pool: The total collection of all alleles for every gene within a population. A diverse gene pool increases the likelihood that some individuals will possess traits necessary for survival if environmental conditions change.

A diagram showing a population with diverse colored circles representing different alleles within a single gene pool.

2. The Role of Mutation

Ultimate Source: Mutation is the primary source of all new genetic variation. It is a rare, random change in the DNA base sequence of a gene or chromosome.
Mechanism of Change: A change in the DNA sequence can alter the sequence of amino acids in a protein. This may change the protein's 3D shape and function, leading to a new phenotype.
Spontaneity: Mutations occur continuously and spontaneously, though their rate can be increased by external factors like ionising radiation (UV, X-rays) or certain chemicals (mutagens).

3. Environmental Selection Pressures

Selection Pressure: External factors such as predation, disease, or climate change that affect an individual's ability to survive and reproduce. These pressures determine which variations are 'advantageous'.
Differential Survival: Individuals with alleles that produce phenotypes better suited to the environment are more likely to survive the 'struggle for existence'.
Reproductive Success: Survival is only evolutionarily significant if the individual reproduces. Advantageous alleles are passed on to the next generation, increasing their frequency in the population.

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions