24 Examples of Population Genetics

Population genetics examples

Population genetics is a branch of biology that focuses on how genetic information in populations changes over time. It helps us understand why populations of animals, plants, and other organisms are the way they are, and how they evolve. In population genetics, we look at different factors that influence the genetic makeup of populations. These factors include natural selection, where traits that are better for survival become more common; genetic drift, where random changes can affect small populations; mutations, which are changes in the DNA that can introduce new characteristics; and gene flow, where genes move between populations, often through migration. By studying these examples and others, population genetics gives us a deeper understanding of the natural world. Here are some examples of population genetics:

Examples

1. Natural Selection

Natural selection

Natural selection is a process through which organisms with traits better suited to their environment are more likely to survive and reproduce. In population genetics, natural selection can lead to a change in the genetic makeup of a population over time. For example, if a certain colouration helps rabbits avoid predators, those rabbits may live longer and have more offspring. Over generations, the gene for that colouration can become more common in the rabbit population. Natural selection shows how environmental factors can shape the genetic diversity of a population, leading to evolutionary changes.

2. Genetic Drift

Genetic Drift

Genetic drift is a change in the frequency of an allele within a population due to random sampling of organisms. An example of genetic drift could be a small group of insects being blown to a new island. Since only a few insects start the new population, their genes represent only a small sample of the original population’s genetic diversity. Genetic drift illustrates how chance events can affect the genetic structure of populations, especially in small populations.

3. Mutation

Mutation

A mutation is a change in the DNA sequence of an organism. For instance, a mutation that occurred in killifish, a freshwater fish discovered on the east coast of the US, made it more resistant to toxic sludge in the water. Mutation demonstrates how new genetic variations are introduced into a population, which can be crucial for the population’s adaptation and evolution.

4. Gene Flow

Gene Flow

Gene flow is the transfer of genetic material from one population to another. An example of gene flow is when pollen from one plant population is carried to another by the wind. This can introduce new genetic material to the receiving population. Gene flow can increase genetic diversity and potentially aid in adaptation and survival.

5. Founder Effect

Founder Effect

The founder effect occurs when a new colony is started by a few members of the original population. A classic example is a small group of people, such as the Amish people, founding a new village. The genetic traits of these founders can disproportionately influence the future genetic pool of the village. The founder effect shows how the genetic makeup of a population can be significantly influenced by a small number of individuals, leading to reduced genetic variation compared to the original population.

6. Bottleneck Effect

Bottleneck Effect

The bottleneck effect occurs when a population’s size is significantly reduced due to environmental events or other catastrophes. For example, if a natural disaster drastically reduces the number of individuals in a cheetah population, the genetic diversity of the population may decrease. This is because only a small number of individuals contribute to the gene pool of the next generation. The bottleneck effect illustrates how population size reductions can lead to a loss of genetic diversity, which can affect the population’s ability to adapt and survive in changing environments.

7. Balancing Selection

Balancing Selection

Balancing selection is a type of natural selection that maintains genetic diversity in a population by favouring heterozygote individuals. An example is the sickle cell trait in humans. Individuals with one copy of the sickle cell allele are resistant to malaria, but having two copies causes sickle cell disease. Therefore, in areas where malaria is common, the heterozygote advantage keeps both the normal and sickle cell alleles present in the population. Balancing selection shows how certain genetic traits can be preserved in a population because they offer a survival advantage in specific environmental conditions.

8. Sexual Selection

Sexual Selection

Sexual selection is a form of natural selection through which certain traits increase an individual’s chances of mating and reproducing. For example, peacocks with larger and more colourful tails are more attractive to peahens. Although these tails are a burden in terms of survival, they are favoured because they increase the male’s reproductive success. Hence, sexual selection highlights how traits that are advantageous for mating can be selected, even if they are disadvantageous in other aspects of survival.

9. Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium

The Hardy-Weinberg Equilibrium is a principle, stating that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences. For example a large and randomly mating population with no mutation, migration, genetic drift, or selection. In such a population, the allele frequencies are expected to remain stable over time. This concept is important as it provides a baseline for measuring genetic change and understanding when and how populations are evolving.

10. Adaptive Radiation

Adaptive Radiation

Adaptive radiation is the process through which organisms diversify rapidly into a multitude of new forms, particularly when a change in the environment makes new resources available. A famous example is the finches on the Galapagos Islands, which evolved from a common ancestor into several species with different beak shapes and sizes, each adapted to different food sources. Adaptive radiation demonstrates how environmental changes can lead to a rapid increase in biodiversity through the process of evolution.

11. Directional Selection

Directional selection

Directional selection occurs when a certain trait is consistently favoured over others, leading to a shift in the population’s overall genetic makeup. For example, originally, the horse population might have varied levels of speed and endurance. However, over time, the faster horses with greater endurance have a survival and reproduction advantage. As a result, their offspring are also likely to inherit traits for greater speed and endurance. Over generations, the average speed and endurance of the horse population increases. Directional selection is significant because it demonstrates how environmental changes can lead to a consistent directional change in a population’s traits.

12. Disruptive Selection

Disruptive selection

Disruptive selection occurs when extreme values for a trait are favoured over intermediate values. An example of this can be seen in a population of Salmon. Disruptive selection in salmon is an evolutionary process in which two extreme traits are favoured over the average traits in a population. In their habitat, some salmon are very large, and some are very small. If the environment benefits these two sizes – maybe the large salmon are better at fighting for mates, and the small ones are better at hiding from predators – then these two types of salmon will thrive and reproduce more. Over time, the number of average-sized salmon decreases because they’re not as good at surviving or reproducing as the large or small ones. This leads to a population in which most salmon are either very large or very small, with few in the middle size. Disruptive selection is important because it can lead to increased genetic diversity within a population and can be a precursor to the formation of new species.

13. Inbreeding

Inbreeding

Inbreeding refers to the mating of closely related individuals, which can increase the chances of offspring inheriting genetic disorders. An example is seen in certain purebred dog populations, in which a small genetic pool results in a high frequency of certain inherited diseases. Inbreeding highlights the risks of reduced genetic diversity, including increased susceptibility to diseases and reduced overall fitness of the population.

14. Heterozygote Advantage

Heterozygote Advantage

Heterozygote advantage occurs when individuals who are heterozygous at a particular gene locus have higher fitness than both kinds of homozygotes. A well-known example is the case of cystic fibrosis carriers. People who are carriers (heterozygous) for the cystic fibrosis gene are more resistant to certain types of tuberculosis, giving them a survival advantage in regions where tuberculosis is common. Heterozygote advantage shows how genetic diversity, even in the form of potentially harmful genes, can confer an advantage under certain environmental conditions.

15. Linkage Disequilibrium

Linkage Disequilibrium

Linkage disequilibrium refers to the non-random association of alleles at different loci in a given population. For example, in a human population, two genes located close together on the same chromosome might be inherited together more often than expected by chance. This can be important in studying inherited diseases, where certain combinations of alleles can indicate a higher risk. Linkage disequilibrium is significant in population genetics as it helps in understanding how genes are inherited together and their potential implications for genetic diseases and traits.

16. Assortative Mating

Assortative Mating

Assortative mating is when individuals in a population choose mates with similar traits to their own. For example, in a bird population, if birds with similar plumage (feathers) colours preferentially mate with each other, this can lead to an increase in the frequency of certain colour traits in the population. Assortative mating can lead to increased genetic similarity within a population and can influence the distribution of genetic traits across generations.

17. Polymorphism 

Polymorphism

Polymorphism in population genetics refers to the occurrence of two or more distinct forms (or alleles) of a gene within a population, such as the blood group polymorphism in humans (A, B, AB, O). These different blood types are maintained in the population because no single type has a consistent survival disadvantage or advantage. Polymorphism represents the genetic diversity within a population and shows how multiple forms of a trait can coexist and be maintained over time.

18. Epistasis

Epistasis

Epistasis occurs when the expression of one gene is affected by the presence of one or more ‘modifier genes’. An example is coat colour in dogs. The expression of one gene determines if the coat will be dark or light, while another gene can modify this trait to determine if the coat will be solid or spotted. Epistasis is important in population genetics because it demonstrates the complex interactions between different genes and how these interactions can affect the traits of organisms in a population.

19. Genetic Hitchhiking

Genetic Hitchhiking

Genetic hitchhiking, or genetic draft, happens when an allele increases in frequency not because it itself is advantageous, but because it is near another gene that is undergoing positive selection. This can occur, for example, when a beneficial mutation arises in a gene, and nearby genes on the chromosome ‘hitchhike’ along with this advantageous gene as it becomes more common in the population. Genetic hitchhiking shows how the fate of one gene can be influenced by linked genes, affecting the genetic landscape of populations in ways not solely determined by natural selection acting on each gene individually.

20. Frequency-Dependent Selection

Frequency-Dependent Selection

Frequency-dependent selection occurs when the fitness of a phenotype depends on how frequently it appears in a population. A well-known example is the scale-eating fish in African lakes. Fish that eat scales off other fish are either left-mouthed or right-mouthed, and their success in feeding depends on the rarity of their type. When one type becomes common, its feeding becomes less successful, and the rarer type increases in frequency. Frequency-dependent selection can maintain genetic variation within a population and demonstrates how the adaptive value of a trait can change depending on its prevalence in the population.

21. Outbreeding Depression

Outbreeding Depression

Outbreeding depression occurs when offspring resulting from matings between genetically distant individuals exhibit lower fitness. For example, in plant populations, crossing between individuals from geographically distant populations can result in offspring that are less adapted to the local environment, exhibiting poorer growth or survival rates compared to offspring from local matings. Outbreeding depression highlights the potential downsides of introducing genetic material from distant populations, which can disrupt local adaptations and reduce overall fitness.

22. Genetic Load

Genetic Load

Genetic load refers to the burden imposed on a population by the accumulation of deleterious mutations. An example can be seen in a population that has undergone a bottleneck or founder effect, where the reduced genetic diversity can lead to an increased prevalence of harmful mutations, reducing the overall health and viability of the population. Genetic load illustrates the impact of deleterious mutations on population health and survival, emphasizing the importance of genetic diversity for the long-term sustainability of populations.

23. Cline

Cline

A cline in population genetics is a gradual change in a trait or genetic variation over geographical space. For instance, in a species of bird, the size of the individuals may gradually increase or decrease over a geographical gradient. This change could be related to environmental factors, such as temperature or food availability, varying across the species’ range. Clines demonstrate how populations can adapt to different environmental conditions across their geographical range, contributing to the diversity within a species.

24. Quantitative Trait Loci (QTL) Mapping

Quantitative Trait Loci (QTL) Mapping

QTL mapping is a method used to identify the locations of genes that are associated with specific quantitative traits, like height or weight. For example, in agricultural research, QTL mapping can be used to find genes in crops that are associated with drought tolerance or yield. This information can then be used to breed crops with desired characteristics. QTL mapping helps in understanding the genetic basis of complex traits and can be applied in breeding programs for the improvement of crops, livestock, and even in medical research.

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