Common Dominant and Recessive Traits in Humans: A Simple Guide
Half of your genetic blueprint that, in large, determines your visible outward characteristics is inherited from your mother and the other half is inherited from your father. This means that you inherit each gene twice, which, you guessed it, means that you have two copies of each gene. These two gene copies are also called alleles, and they come in two forms: dominant and recessive.
Dominant and Recessive Alleles Defined
A dominant allele will result in a dominant phenotype. This is regardless of whether there are one or two copies of the allele present. In other words, one copy of the dominant allele is enough for it to manifest itself as a trait. This means that it can come from just one parent—think about brown-eyed children of brown-eyed mothers (brown eyes are based on a dominant allele, while blue eyes are recessive). A recessive allele results in a recessive phenotype only if a person carries two copies of it. This means that someone who has a dominant allele and a recessive allele will have the dominant phenotype. However, these individuals are still considered to be carriers of the recessive allele.
The concepts of dominant and recessive are practical in the prediction of inheritance of a certain trait. This is especially useful when it comes to certain disorders. However, these used to be quite confusing before the scientific community knew how to determine the underlying DNA. Still, it is important to point out that there is no specific way by which dominant and recessive genes behave. The term “dominant” does not literally indicate dominance or repression. Rather, it all depends on the behaviors of the proteins that these genes code for.
Common Dominant Traits
There are fairly common dominant inherited human traits, known as inheritance patterns, within the human population, and some examples are listed below.
Long eyelashes are a hot and desired trend these days. Lucky for us, the gene that codes for long lashes is dominant, whereas the one that codes for short lashes is recessive. Babies With a dark hair color will have long lashes that are a lot more prominent than those of light-haired offspring. Furthermore, parents who have dark hair and long lashes have a much higher chance of having babies of the same inherited traits.
Dimples are among the more adorable dominant traits. Little did you know that those little indentations in the cheeks are actually inheritable. Therefore, if both mom and dad have dimples, chances are pretty high that the baby will have them, too. Given that it is a dominant trait, chances are pretty high that the baby will have dimples even if just one parent has them. And while the chances are lower in this scenario, even if neither of the parents has dimples, the baby may still have them as a result of grandparents having had them (the biology of that is a bit beyond this post, but it is still good to know).
The ability to taste phenylthiocarbamide (PTC) is dominant. PTC, found in certain vegetables such as cabbage, brussels sprouts, and broccoli, is bitter to those who can taste it, while those who cannot do not taste anything. A gene on chromosome 7 drives the dominant ability to taste PTC. In fact, four out of the five alleles are responsible for tasters while one of the five alleles codes for the inability to taste PTC.
Common Recessive Traits
There are also fairly common recessive traits within the human population, and some examples are listed below.
The gene that codes for red-green color blindness resides on the X-chromosome and it codes for a protein in the eye that is responsible for detecting specific colors of light. In the case of a defect within the gene, the eye is not able to distinguish between the colors green and red. Since two copies of the defective form of the gene are needed for an individual to be color blind, females need to inherit each copy from both the parents, whereas males who inherit their copy from the mother will always be color blind. As such, color blindness affects males a lot more than females.
Did you know that having five fingers is actually a recessive trait? How did it happen that a trait that is not dominant took over? It is not quite known yet, but it turns out that having six fingers is a dominant trait, while having the more common trait of five fingers is actually recessive. So, while it is true that having six fingers is dominant, five-fingered individuals are far more common than their dominant-trait counterparts, which is why there are many more five-fingered individuals than there are six-fingered ones.
Being Single Jointed
This may come as another surprise, but being single-jointed is actually recessive while being double-jointed is dominant. Little did you know that those individuals who are “extra bendy” are actually bragging about a dominant trait. Double-jointedness is a lot less likely to affect European populations. However, in all honesty, there is no such thing as physically being double-jointed. As noted on the BBC website (2015): “For humans at least, there is no such thing as being double-jointed. Those bendy-bodied boasters? They’re just impressively flexible.”
The inability to hear a tune or follow a tune, whether that is through singing or dancing, is actually a dominant trait. Therefore, those of us who can sing and dance and follow rhythm can actually do so because we possess two copies of the gene that codes for “having rhythm.” Now we can feel even more special about it. Furthermore, it should be added that being tone deaf is a result of several genes working together, which culminates in the exact degree of tone-deafness for each individual.