Up to this point, we have explored the fundamentals of genetics, such as where DNA is located, how it is structured, how mutations arise, how proteins are formed through transcription and translation, and how genes are expressed. These concepts form the building blocks of molecular biology. Now, it’s time to take this knowledge to a broader level and apply it to entire groups of individuals. This field of study is known as population genetics.

If we have to define it in simple words, population genetics is “a branch of genetics that studies how genetic variation is distributed and how it changes within populations over time.” It acts as a bridge between Mendelian genetics and evolutionary biology, offering a mathematical framework to understand how genes evolve under different environmental and evolutionary pressures.

Population

Before we dive deeper into the different aspects of population genetics, the first step is to clearly define what we mean by a population.

In biology, a population is simply a group of individuals of the same species living in the same area who can interbreed with each other. For example, all the humans in a city, all the tigers in a forest, or all the frogs in a pond can each be considered a population.

But in genetics, the meaning goes a little deeper. Here, a population is not just about living together but it’s about sharing genes. All the genetic material carried by the individuals of a population forms a collective storehouse called the gene pool. This gene pool is like a library of genes, where each individual represents a unique combination borrowed from the same collection.

One of the fundamental principles of population genetics is the Hardy-Weinberg Equilibrium (HWE), which describes an idealized population where allele frequencies remain constant over generations in the absence of evolutionary forces such as natural selection, mutation, genetic drift, gene flow, and non-random mating. The Hardy-Weinberg equation, p2+2pq+q2=1, estimates allele and genotype frequencies in a population and determines whether it is evolving.

Various evolutionary forces influence genetic variation in populations. Mutation introduces new alleles, providing raw material for evolution. Natural selection favors beneficial alleles, increasing their frequency over time. Genetic drift, a random change in allele frequencies, is more pronounced in small populations and can lead to loss of genetic diversity. Gene flow, or migration, introduces new alleles into a population, promoting genetic diversity. Lastly, non-random mating affects genotype frequencies by favoring certain traits over others.

Population genetics has significant applications in various fields, including medicine, conservation biology, and evolutionary studies. It helps scientists understand the genetic basis of diseases, track the evolution of antibiotic resistance, and develop conservation strategies for endangered species by assessing genetic diversity. Understanding how genetic variation operates within populations is crucial for predicting evolutionary trends and maintaining biodiversity.

The gene pool is the total collection of all genes and their alleles in a population at a given time. It represents the genetic diversity of that population.

A larger gene pool means greater genetic variation, which helps populations adapt to environmental changes and survive. A smaller gene pool can lead to reduced adaptability and increased risk of genetic disorders.

Example of a Gene Pool

Example 1: Eye Color in a Village

Imagine a village with 100 people, where eye color is controlled by a single gene with two alleles:

• B (brown eyes) – Dominant

• b (blue eyes) – Recessive

The population has the following distribution:

• BB (homozygous brown-eyed) = 40 people

• Bb (heterozygous brown-eyed) = 50 people

• bb (homozygous blue-eyed) = 10 people

Gene Pool Analysis

Each person has two copies of the gene (one from each parent), so there are 200 total alleles in the population.

• B alleles in the population:

  • BB = 40 × 2 = 80

  • Bb = 50 × 1 = 50

  • Total B alleles = 80 + 50 = 130

• b alleles in the population:

  • Bb = 50 × 1 = 50

  • bb = 10 × 2 = 20

  • Total b alleles = 50 + 20 = 70

Thus, the allele frequencies in the gene pool are:

• Frequency of B (p) = 130/200 = 0.65 (65%)

• Frequency of b (q) = 70/200 = 0.35 (35%)

This shows how the gene pool consists of all copies of each allele in the population and how we can measure their distribution.