Population Genetics

Population Genetics

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Population genetics the study of genetic variation in groups of organisms from the same species. Even if they look similar, each individual has unique genetic information that determines their traits like height or flower coloration in plants. To study these differences, we look at the gene pool, which is the total set of genes and alleles for all organisms in a population. By analyzing the frequency of genes and alleles over time and space, we can determine genotype, phenotype, and allele frequencies. This field combines Gregor Mendel's principles with Darwin's theory of evolution by natural selection. For example, in humans, eye color is determined by genes inherited from our parents. Brown eyes are dominant over blue eyes, so even if someone has one allele for each color, their eyes will be brown. The study of population genetics helps us understand how and why organisms evolve over time.

Population Genetics Example

Let's use a plant population as an example to understand population genetics. Imagine there are 1000 plants, and some have purple flowers while others have white flowers Researchers found that there are two alleles for this trait: one dominant and one recessive. They studied the genetic composition of all the plants and found that 460 have the dominant allele and purple flowers, 430 have one of each allele and purple flowers, and 110 have the recessive allele and white flowers.

In population genetics, alleles are usually represented by letters. A dominant allele is shown with a capital letter (A), while the corresponding recessive allele is shown with a lowercase letter (a). To find the frequency of a trait, we count the number of individuals with that trait and divide by the total number of individuals in the population. For example, the frequency of purple flowers would be (460 + 430) / 1000 = 0.89.

The total frequency of any trait is always 1. This means that the frequencies of all genotypes in a population add up to 1 (AA + Aa + aa = 1), and the same for alleles (A + a = 1 Frequ range 0 to . A frequency of 0 means an allele is not present the population, while a frequency of 1 means the allele is the only one present, which is called being fixed in the population.

Factors Affecting Population Genetics

The frequencies of alleles and genotypes in a population can change over time, which means the population is evolving. This process is called microevolution and can occur through natural selection, mutation, nonrandom mating, genetic drift, and genetic flow. Natural selection acts on individuals, but the population as a whole evolves. A population in which allele and genotype frequencies do not change is in Hardy Weinberg equilibrium. These processes can increase or decrease genetic variation, allele frequency, or adaptation, and their effects can vary depending on the situation. Therefore, population genetics is influenced by many factors that can shape the evolution of a population over time.


Mutations are changes in the DNA sequence that can produce new alleles and are the basis for genetic variation. These changes occur unpredictably at the individual level and must be heritable to have a long-term effect on the population. Mutations that occur in somatic cells do not affect the next generation, but mutations in reproductive cells can be passed on to offspring. Although mutations are important for creating genetic variation, they do not happen frequently enough to significantly affect allele frequency on their own. However, mutations can have a significant effect on the population when other evolutionary mechanisms such as natural selection act on them.

Nonrandom Mating

Nonrandom mating is a process in which individuals do not have an equal chance of mating with any other individual in the population. Instead, they may choose mates based on certain characteristics, such as physical traits or proximity. This process can affect the genotype frequencies within a population, but not the allele frequencies. As a result, nonrandom mating may not have a significant effect on the overall evolution of the population. However, it can lead to certain traits becoming more common in future generations if individuals with those traits are more likely to mate and pass on their genes. Therefore, while nonrandom mating may not be a major driver of evolution, it can still play a role in shaping the genetic makeup of a population over time.

Genetic Drift

Genetic drift is a random change in the allele frequencies within a population. It causes a reduction in the genetic variability in the population, and the changes caused by genetic drift are usually not adaptive (because they are random, caused by chance). Random natural disasters such as hurricanes, flooding, or landslides can affect animal and plant populations. Many individuals may die due to these random events, even if they are well adapted to their environment. The key factor here is that these drift effects are stronger in small populations because a dramatic reduction in an adaptive allele or genotype can decrease the overall fitness of that population. It is less likely that a large will a significant percentage of these adaptive alleles or genotypes. A sudden reduction in population size (and its genetic variability) caused by adverse environmental conditions is a bottleneck. When a small part of a population colonizes a new area, it is called the founder effect.

Gene Flow

Many animals move from their birth population to a different one during the breeding season; this is a type of migration. Migrants can introduce a new allele to a population, or if it carries the same alleles already present in the population, they can change the frequency of the allele. Gene flow is a movement of alleles between populations and can cause changes in allele frequency Interchanging between two tend and hence, genetic flow usually decreases the differences or variations between these populations. However, gene flow can also have negative consequences, such as introducing harmful alleles into a population or disrupting local adaptations.

Gene flow can occur through a variety of mechanisms, including dispersal of seeds or pollen, movement of individuals, or even accidental transport by humans. In some cases, gene flow can be restricted by geographic barriers, such as mountains or bodies of water, which can lead to the formation of distinct populations that may evolve in different ways over time.

Overall, gene flow is an important factor in the evolution of populations and can have both positive and negative effects on the genetic diversity and adaptation of populations.

Natural Selection

The genotypes (and corresponding phenotypes) with greater survival and reproduction probabilities for a specific environment will contribute more offspring to the next generation through natural selection. Natural selection causes a change in adaptive allele frequency, resulting in higher survival and reproduction probabilities. Natural selection acts on the phenotype of an individual, but it is the population that adapts to a particular environment.

Population genetics assesses the genetic variation within populations. This occurs mainly by determining the frequency of alleles and genotypes and whether these change over time and/or space. In population genetics, a frequency of 0 means that an allele is not present in the population, while a frequency of 1 means the allele is the only one present. In this case, the allele is fixed in the population.

It is common for allele frequencies in a population to change over time, which means a population has evolved. Natural selection is not the only way evolution occurs; other evolutionary processes are mutation, non-random mating, genetic drift, and genetic flow.

Mutations are the basis for genetic variability on which natural selection acts since mutations can produce new alleles. For a mutation to have a long-term effect on the population, it must be heritable and transmitted to subsequent generations. In other words, it must occur in reproductive cells (gametes = sperm or eggs).

Non-random mating usually changes the genotype frequencies within a population, but not the allele frequencies.

Genetic drift causes a reduction in the genetic variability of the population. Usually, these changes are non-adaptive (because they are random, caused by chance). These effects are stronger in smaller populations than in larger populations.

Genetic flow usually makes populations more similar (decreases the difference or variation between populations). However, gene flow can also have negative consequences, such as introducing harmful alleles into a population or disrupting

Population Genetics

what is population genetics?

Population genetics is the study of the genetic variability among the individuals within and between populations, and the evolutionary mechanisms that influence this variability.

what is the biological significance of genetic diversity between populations?

The biological significance of genetic diversity between populations is that each population is more fit to local conditions, according to the combination of traits that gave them an advantage in that environment. Moreover, maintaining genetic diversity allows a population to adapt to future changes in the environment.

what causes genetic variation in a population?

There are three main sources of genetic variation in a population: mutations (create new genes/alleles), gene flow/migration (introduce new genes/alleles), and sexual reproduction (create new combinations of genes/alleles). 

how does genetic diversity affect a population's chances of survival?

Genetic diversity increases a population´s chances of survival by providing a more diverse array of traits that increases the probability of some individuals in the population to adapt to changing environmental conditions and pass on these traits to the next generations.

how is genetic variation maintained in most populations?

Genetic variation can be maintained in most populations through the same mechanisms that can increase it: mutations, gene flow/migration, and sexual reproduction. Another important factor would be shifting environmental or external conditions, as selection would favor different genotypes adapted to specific conditions at a different time or space.

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