What is High Genetic Diversity and Why Is It Important?

Genetic diversity is the spectrum of different inherited traits within a species. A population with a wide range of these traits has high genetic diversity, which provides the foundation for adapting to shifting environmental conditions.

What Constitutes High Genetic Diversity?

High genetic diversity is characterized by a large number of different versions of genes, known as alleles, within a population’s gene pool. This richness provides the raw material for natural selection, allowing for a wide array of physical and physiological differences among individuals.

Scientists measure this diversity using several methods. One approach is assessing heterozygosity, which measures the proportion of individuals carrying two different alleles for a specific gene. Another method is measuring allelic richness, which counts the number of different alleles present at a specific genetic location.

This variation manifests in numerous ways, from visible traits like color and size to internal functions like metabolic efficiency and immune system responses. For instance, a plant population with high genetic diversity might include individuals with varying tolerances to drought, heat, or certain pests.

Natural Processes That Foster Genetic Richness

The source of all new genetic variation is mutation, which involves random changes in an organism’s DNA sequence. These changes can introduce new alleles into a population, expanding the gene pool. While many mutations may be neutral or harmful, some can produce beneficial traits that enhance an organism’s ability to survive and reproduce. The rate of mutation can influence the level of genetic variation, particularly in species with rapid reproduction.

Sexual reproduction is another mechanism for increasing genetic diversity. During meiosis, the process that produces sex cells, homologous chromosomes exchange genetic material in a process called crossing over. This shuffling of existing alleles, combined with the random assortment of chromosomes, creates new combinations of genes in the offspring.

Gene flow, or the migration of individuals between populations, also plays a role. When individuals move to a new area and interbreed with the local population, they can introduce new alleles or alter the frequencies of existing ones. This process increases diversity within the recipient population and counteracts the isolating effects of genetic drift.

Adaptive Strength in Genetic Variation

High genetic diversity provides a population with the flexibility to adapt to changing environmental conditions. When an environment shifts due to climate change, new pollutants, or a new predator, a genetically diverse population is more likely to contain individuals with traits suited for survival. These individuals are more likely to reproduce, passing their advantageous alleles to the next generation.

This principle is evident in disease resistance. A population with varied immune responses is less vulnerable to being devastated by a single pathogen. If a disease emerges, some individuals may possess genetic resistance, allowing them to survive and rebuild the population. The koala’s low genetic variability, for example, has been linked to its susceptibility to diseases like Chlamydia and the koala retrovirus (KoRV).

A diverse gene pool also mitigates the effects of inbreeding, the mating of closely related individuals. Inbreeding is more common in small populations and can lead to a reduction in fitness. This happens when offspring are more likely to inherit two copies of a harmful recessive allele. High genetic diversity reduces the chances of this occurring, promoting population health.

Pressures Reducing Genetic Variability

Genetic drift, the random fluctuation of allele frequencies from chance events, reduces genetic diversity, especially in small populations. This can lead to the loss of certain alleles while others become fixed, meaning they are the only version of that gene left. This process is not driven by natural selection and can result in the loss of beneficial traits by random chance.

Population bottlenecks occur when a population experiences a drastic reduction in size from events like natural disasters or overhunting. The few survivors may not represent the full genetic spectrum of the original population, leading to a loss of diversity. The northern elephant seal, for instance, was hunted to near extinction in the 1890s. Its rebounded population has much lower genetic variation than the southern elephant seal.

A similar phenomenon, the founder effect, occurs when a new population is established by a small number of individuals. This founding group may have a non-representative sample of the original population’s genes, resulting in lower diversity. This is seen in the Afrikaner population of South Africa, which has a high frequency of Huntington’s disease due to the makeup of the original Dutch colonists.

Human activities, such as habitat fragmentation and selective breeding, also contribute to the loss of genetic variability by isolating populations or narrowing the gene pool.

Protecting Our Genetic Heritage

Conserving genetic diversity requires protecting populations and their habitats. Establishing protected areas like national parks and wildlife reserves helps maintain large, interconnected populations where gene flow can occur. Restoring degraded habitats and creating wildlife corridors can reconnect fragmented populations, allowing for the exchange of genetic material.

For species with low diversity, species-specific programs are often necessary. Captive breeding programs can maximize genetic diversity by carefully selecting mating pairs to avoid inbreeding and ensure representation of the remaining gene pool. In some cases, genetic rescue, which involves introducing individuals from a different population, can augment the genetic health of a struggling population. These efforts require genetic monitoring to track changes over time.

Another strategy involves genetic resource banking. This includes the cryopreservation of materials like seeds and tissues in gene banks and seed storage in facilities like the Svalbard Global Seed Vault. These repositories safeguard genetic material for future research, breeding programs, or reintroduction efforts.