Why Are Certain Traits More Dominant?

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Why Are Certain Traits More Dominant?

Traits are more common the more copies there are of that gene version, called the allele, there are in a population / Photo by Getty Images

 

When we look at our parents, we can often compare and contrast the different traits that we’ve inherited from them, such as the quality of our hair and height.

From science classes, we know that certain genes can be more dominant than others. But the question is: Why?

 

The Basics of Genetics

Many of us learned in past lessons in biology that the traits that creatures have, especially humans, are passed down through genes that we inherit. We also found out that as there are a great number of different genes, which account for the genetic variety, there are some genes that are considered “dominant” and others are recessive. Dominant traits will often dominate over other traits, such as brown eyes being more dominant than blue eyes, and black hair being more dominant than red hair.

The father of genetics, the Austrian monk Gregor Mendel, was the first to realize that traits could be passed down from parents to their offspring after he studied pea plants. By cross-breeding those with the same traits, such as ones with the same height, seed shape, or flower color, he proved that the offspring would have the same traits as the parent plants.

He also found out that if the offspring inherited both flavors of the genes, for example, one “tall” gene and one “short” gene, the offspring would exhibit the dominant trait, which in this case is the tall gene. However, as explained by the Washington Post, a percentage of the offspring could possibly have the gene not dominantly shared by both parents.

 

Dominant is Not Common

Many people tend to believe, then, that those dominant traits are more common but that is not the case at all. Traits are more common the more copies there are of that gene version, called the allele, there are in a population. Being dominant or recessive has no bearing on how often you see it in the population.

One example is this is the countries in Africa versus those in Northern Europe, as explained by KQED Science. Almost all people in Africa have brown eyes, while about 80% of people in Northern Europe have light-colored eyes. The fact that brown eyes are common in Africa isn’t because brown is a dominant allele. The gene that determines whether you have brown eyes or not is called OCA2. It has two versions: the brown allele and the not-brown allele. It so happens that the brown allele is dominant.

Many human traits, such as eye color, are influenced by more than just one simple gene / Photo by Getty Images

 

The population in Africa happens to have a great number of people who have the brown allele of OCA2. The reverse is true in Northern Europe. The not-brown allele is more common, though it is recessive. There are still a number of brown-eyed people in that area. However, the dominant allele doesn’t truly shine if it is being overwhelmed by recessive genes. If a brown-eyed and light-color eyed person marry, it’s likely that the brown color of the eyes will show in their children. But since the population has an abundance of persons with light-colored eyes, they tend to have children that reflect their own genes. Over time, however, some genes can become more or less common, depending on how people pass on their genetics.

 

Why is There Dominance?

There isn’t one single answer as to why certain traits are dominant over others, and why these would prove useful. Many human traits, such as eye color, are influenced by more than just one simple gene. As we are much more complicated than pea plants, there is no easy way to map out the possible change with just a Punnett square. Some combinations of different alleles will produce the same proteins that will bring about a certain trait, even if we didn’t necessarily inherit it.

Going back to the example of eye color, one gene that determines it is the gene that controls melanin pigment production in the eye, which is the substance that also brings color to our skin. If one happens to inherit the “turned-off” variety, that means they are more likely to inherit lighter-colored eyes as these would have less pigment in them. However, other genes will also determine what hue these light-colored eyes will have.

Genes and Diseases

The complexity of genes and their alleles have a great part to play in inheriting certain health disorders and how serious they are. In sickle-cell anemia, those who have two copies of the allele for the condition end up having damaged red blood cells that are unable to perform their jobs well, which leads to life-threatening situations. Those who only have a single copy will have a number of malformed cells, but ultimately the healthy cells are able to keep functions normal.

However, the sickle-cell alleles are technically “dominant” ones, as having even a single copy can produce noticeable effects, such as giving one protection over malaria.

Over the years, scientists have been able to uncover the inner workings of genetics and have used this knowledge to determine whether one would have a certain genetic condition, which has given rise to genetic counseling that has helped many lives.

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