How does genetic diversity differ from species diversity?

Genetic diversity refers to the variation of alleles within a single species or population. Species diversity refers to the number of different species and their relative abundance within a specific community or ecosystem.

What is the difference between a gene and an allele in the context of diversity?

A gene is a section of DNA that codes for a specific polypeptide or trait shared by all members of a species. An allele is a specific version of that gene; diversity is measured by how many different alleles exist for a gene in a population.

How does a large gene pool compare to a small gene pool regarding extinction risk?

A large gene pool contains many different alleles, increasing the chance that some individuals can survive environmental changes. A small gene pool lacks this variety, making the entire population vulnerable if conditions change, potentially leading to extinction.

Why is it incorrect to say that an environment 'causes' a beneficial mutation to appear?

Mutations occur randomly due to errors in DNA replication or mutagens, regardless of environmental needs. The environment only acts as a filter (selection pressure) that determines which pre-existing mutations are advantageous.

What is the mistake in defining fitness as 'being the strongest or fastest'?

In biology, fitness is strictly the ability to survive and pass on alleles to offspring. A 'strong' individual that fails to reproduce has a biological fitness of zero because its alleles do not persist in the gene pool.

Why might a new mutation not result in a change to the phenotype?

The genetic code is degenerate, meaning multiple DNA triplets can code for the same amino acid. If a mutation changes a triplet to another that codes for the same amino acid, the protein structure and phenotype remain unchanged.

Define 'Genetic Diversity'.

Genetic diversity is the total number of different alleles of genes in a population. It is a measure of the genetic variation present within a specific group of organisms.

What is a 'Gene Pool'?

A gene pool is the complete set of all the alleles for all the genes in a specific population at a given time. It represents the total genetic information available for the next generation.

What is meant by 'Allele Frequency'?

Allele frequency is the fraction or percentage of all chromosomes in a population that carry a specific allele. Evolution is often defined as the change in these frequencies over time.

How do mutations contribute to the process of natural selection?

Mutations create new alleles, which lead to phenotypic variation. If a new phenotype provides a survival advantage under specific selection pressures, those individuals reproduce more successfully, increasing the allele's frequency.

Genetic Diversity | AQA A-Level Biology

Genetics, Variation & Interdependence

Genetic Diversity

Summary

Genetic diversity represents the total number of different alleles of genes within a specific population. It serves as the fundamental biological substrate for natural selection, enabling populations to adapt to fluctuating environmental pressures and reducing the risk of species extinction.

1. Definition & Core Concepts

Genetic Diversity is formally defined as the total number of different alleles of genes present within a population. While individuals of the same species share the same genes, the specific versions (alleles) they possess vary due to differences in DNA base sequences.
The Gene Pool refers to the complete set of unique alleles in a population at any given time. A larger, more diverse gene pool provides a wider range of phenotypes, which increases the likelihood that some individuals will possess traits suited for survival in changing conditions.
Allele Frequency is the proportion of a specific allele relative to all other alleles for that gene in the population. Changes in these frequencies over generations are the primary mechanism of evolutionary adaptation.

A diagram representing a gene pool as a contained space filled with diverse alleles (represented by different colored circles), illustrating the concept of genetic variation within a population.

2. Underlying Principles of Variation

Random Mutation is the ultimate source of genetic diversity. A mutation involves a change in the DNA base sequence of a gene, which can result in the creation of a entirely new allele.
The Degenerate Nature of the genetic code means that some mutations (silent mutations) do not change the resulting amino acid sequence. Consequently, a new allele may be genetically distinct without immediately altering the organism's phenotype.
Mutations can be categorized as advantageous, disadvantageous, or neutral. An advantageous allele increases an individual's fitness, making it more likely to be passed on to the next generation through reproductive success.

3. Methods of Adaptation

Natural Selection acts upon existing genetic diversity. When environmental conditions change, individuals with alleles that confer a survival advantage are more likely to survive and reproduce.
Differential Reproductive Success ensures that advantageous alleles are inherited by offspring. Over many generations, the frequency of these beneficial alleles increases within the population's gene pool.
Selection Pressures, such as predation, disease, or climate change, determine which phenotypes are favorable. Without sufficient genetic diversity, a population lacks the 'raw material' for this selective process to occur.

4. Key Distinctions

5. Exam Strategy & Tips

6. Common Pitfalls & Misconceptions