Question

Explain why a gene variant that is present at a high frequency in a population is less likely to be harmful than a very rare variant in that population.

Short answer

A gene variant that is present at a high frequency in a population is less likely to be harmful because natural selection tends to eliminate harmful variants from populations. Therefore, common variants are usually not harmful. On the other hand, rare variants might be harmful, as they have not yet been eliminated from the population or they are new potentially harmful variants.

Step-by-step solution

Understanding Gene Variants

The first part of solving this problem involves understanding gene variants. Every individual carries unique variations in their genes compared to others. These variations are called gene variants. Although some variations can be harmful, most are neutral or even beneficial.

Population Genetics

This is the study of how genetic composition of populations changes over time. If a gene variant gives an organism a survival or reproductive advantage, the frequency of that variant in the population will increase over time due to natural selection.

Frequency of Harmful Variants

Harmful gene variants usually decrease an organism's chances of survival or reproduction, so these variants become less common in the population over time. Additionally, harmful gene variants may arise occasionally through mutation, but they remain rare unless there are other factors at play.

High Frequency Variants Vs Rare Variants

If a gene variant is common in a population, it is more likely that the variant is not harmful. This is because harmful variants tend to be weeded out by natural selection over time. Conversely, if a gene variant is extremely rare, it is more likely to be harmful, as it has not yet been eliminated by natural selection, or it is a new variant that has arisen recently (potentially harmful)

Key concepts

Gene Variants

Gene variants are the different versions of a gene that occur within a population. Each individual has unique sets of these gene versions, resulting in a natural diversity among species. For instance, the gene that determines eye color has several variants, leading to various eye colors.
It is important to understand that not all gene variants have the same impact. Some might lead to noticeable changes in an organism's physical appearance or behavior, while others might be neutral, causing no apparent effect.

• Neutral variants do not affect an individual's survival or reproduction.
• Beneficial variants can enhance an individual's survival or reproductive chances.
• Harmful variants may reduce an individual's fitness and its chances of surviving or reproducing.

Gene variants contribute significantly to the genetic fabric of a species, playing a vital role in how populations evolve over time.

Natural Selection

Natural selection is a key mechanism of evolution. It describes the process by which certain traits become more common in a population due to the advantages they provide.
When a particular gene variant provides a benefit to the individuals carrying it, allowing them to survive or reproduce more effectively than others, natural selection will favor this variant. Over generations, the frequency of beneficial variants increases, while harmful ones decrease.
Natural selection acts like a filter:

• It amplifies traits that improve survival or reproductive success.
• It reduces the occurrence of traits that are detrimental to survival or reproduction.

In this way, natural selection helps mold the genetic structure of populations, ensuring that species adapt to their environments over time.

Genetic Variation

Genetic variation refers to the diversity in gene variants present within a population. This variety is essential for a population's adaptability and resilience to changing environments.
When new environments or challenges occur, genetic variation allows some individuals to possess advantageous traits for survival and reproduction.
Genetic variation arises in several ways:

• Mutations introduce new gene variants.
• Meiosis and sexual reproduction shuffle genes, creating unique combinations.
• Gene flow, which is the exchange of genes between populations, also adds to the diversity.

A rich genetic variation ensures that a species has a better chance of adapting to different pressures and surviving over time. Thus, it is a critical component of a healthy, thriving population.

Harmful vs Beneficial Mutations

Mutations are changes in the DNA sequence of a gene. They are one of the primary sources of genetic variation. However, their effects can vary widely:

• Harmful Mutations: These negatively impact an individual's ability to survive or reproduce. As a result, they tend not to persist in the population due to natural selection.
• Beneficial Mutations: These offer some advantages, such as improved health or reproductive success, making individuals with these mutations more likely to thrive.

Most mutations are neutral with no significant impact. Over time, beneficial mutations become more common as they enhance survival, while harmful ones fade due to natural selection pressures.
Thus, within a population, a common gene variant is more likely to be non-harmful or beneficial, reflecting that harmful mutations have been effectively filtered out. Conversely, rare variants have not gone through extensive selection and may still be potentially harmful.