Why are dominant traits rare?

One of the first things we’re taught in genetics is that some traits are dominant and others are recessive. And that the dominant traits trump the recessive ones. Whether or not a trait is common has to do with how many copies of that gene version (or allele) are in the population.

Can a dominant trait be rare?

Some dominant genes are rare, meaning that a small subset of humans have the dominant allele. The polydactyly trait — having extra fingers or toes — is one example of a rare inherited dominant gene trait.

Are dominant traits more common in a population?

Dominant traits are the most common traits in a population. When people hear the word “dominant”, often they incorrectly believe that the majority of the population expresses this trait. Describing a trait as dominant does not mean it is the most common; it means that it is expressed over the recessive trait.

Is the dominant allele always the most common in a population?

A widespread misconception is that traits due to dominant alleles are the most common in the population. While this is sometimes true, it is not always the case. For example, the allele for Huntington’s Disease is dominant, while the allele for not developing this disorder is recessive.

Why are recessive traits more common?

Recessive disease mutations are much more common than those that are harmful even in a single copy, because such “dominant” mutations are more easily eliminated by natural selection.

Why are some dominant traits such as polydactyly not common?

Whether an allele is common or rare in a population does not depend on whether the allele is dominant or recessive. Dominance occurs when one allele masks the phenotype of another allele. In the case of polydactyly, an allele can become rare when the resulting phenotype is not an advantage for the organism.

Why are some traits dominant?

When we talk about genes being dominant or recessive, we’re generally talking about traits controlled by the amount of a certain protein produced. If genes are controlling a process where all of the alleles need to be on the same page in terms of protein production, the dominant gene will be the one that’s broken.

Why are some traits dominant and recessive?

The two alleles for a gene don’t need to be the same. The instructions you get from your mom can be a little different from the instructions you get from your dad. And these different instructions — or alleles — will end up making slightly different proteins. This is where dominant and recessive come from.

Do dominant alleles automatically become more common in a population over time?

In natural selection, having a certain trait makes an individual more reproductively successful than individuals lacking the trait. Thus, the allele that codes for the favored trait is passed on to more offspring, and becomes more common over time. The result: the frequency of the dominant allele goes up over time.

Why dominant gene is dominant?

​Dominant. Dominant refers to the relationship between two versions of a gene. Individuals receive two versions of each gene, known as alleles, from each parent. If the alleles of a gene are different, one allele will be expressed; it is the dominant gene.

Why are dominant genetic disorders more rare than recessive disorders?

Why are recessive traits more common in some cases?

Why is the dominant trait not always the most common?

From this, people often jump to the conclusion that the dominant trait is also the most common one. This isn’t always the case and there is no reason it should be. Whether or not a trait is common has to do with how many copies of that gene version (or allele) are in the population.

How common is an allele if it is not dominant?

Whether an allele is dominant or not does not affect how common a trait is. Now of course traits can become more common over time. The changes just don’t have anything to do with whether the trait is dominant or not. If brown eyes gave an advantage, then it would start to become more common.

Is polydactyly a dominant or recessive trait?

But polydactyly can also be one symptom of a larger syndrome. In these cases the syndrome (and the polydactyly that comes with it) is usually a recessive trait. Of course this means, in these cases, having five fingers is the dominant trait.

Is having an extra finger dominant or recessive?

When people or animals are born with extra fingers this typically dominant trait is called polydactyly. The same is true for the much more rare ectrodactyly, when people are born missing digits. The exception is when extra or fewer fingers and toes are one part or a larger syndrome. Then polydactyly and ectrodactyly are recessive traits.