Introduction
When someone inherits a recessive trait, you might feel envious of or sympathetic towards them. Why is this the case? Are all the dominant traits much superior to the recessive ones? Well, you’ll be surprised to find out that that’s factually untrue.
The term “dominant” refers to a population that’s more likely to genetically inherit a trait based on their environment. And “recessive” is just the opposite of that. However, these terms are often overlooked from their true definitions.
For a dominant trait to be expressed, two dominant alleles or at least one dominant allele must be inherited. As for a recessive trait to be expressed, both copies of the recessive allele must be inherited. Only obtaining one copy doesn’t work. The dominant trait, if expressed, does not repress the recessive trait because they don’t directly interact with the expression of the recessive allele. Instead, it comes down to what kind of proteins the dominant and recessive alleles are coding for.
It’s the number that counts!
Predicting eye color is easy! Out of the 16 different genes that determine eye color, the two main influences are on the 15th chromosome. In contrast to Type 2 diabetes, at least 150 DNA variations would play a role in triggering the trait. Type 2 diabetes is when the body’s usage and production of insulin isn’t processed as normal, in which insulin is used to control glucose intake into blood cells. Type 2 diabetes hasn’t been clarified as to what’s truly causing people to obtain it, however, both genetic and lifestyle factors do play a role. That said, inheritance patterns are usually more complex for most traits.
Term Swap?
We did bring up environmental factors as one of the contributing factors to influence a population’s dominant and recessive traits. If a population’s increased involvement in one trait to be coded and expressed, it’s labeled as a dominant trait. However, that trait could be reversed to recessive if let’s say, the temperature dropped, or the soil has thawed after winter. Like, how polar bears need to have more fur to layer themselves from the cold and give them warmth.
In the case of Northern Europe’s population on eye colors, Dr. Barry Starr researched: “In some parts of the continent, over 80% of the population has lighter colored eyes. Here [Northern Europe] the not-brown allele is more common even though it is recessive.” Despite the brown-colored trait that’s known to be dominant universally, it’s being applied based off your community’s dominant genetic phenotype. If you’re in Africa, you probably have darker colored eyes because there’s already many Africans that inherited dark-colored eyes from their parents. For the environmental factors, there are multiple theories as to why Northern Europeans have lighter eye colors. However, the two most popular arguments are about the natural selection and sexual selection of their environment. Though, that’s another analysis for another time!
Dominant Diseases
To address the stereotype of recessive genes having the most likelihood to carry diseases, diseases like Huntington’s exist. Huntington’s disease (HD) causes uncontrolled movements of a person when the nerve cells in areas of their brain, controlling voluntary movement gradually break down. Symptoms include physical struggles like walking, cognitive changes like solving problems, and behavioral problems like mood swings. According to the National Institute of Neurological Disorders and Stroke, there’s a 50% chance of inheritance from one parent that has HD and inherits “the copy of chromosome 4 that carries the HD mutation.” The mutation in the gene’s caused by cytosine, adenine, and guanine to repeat abnormally past 36 times when building the DNA. Since HD is commonly found in countries of European origins, it’s a dominant disease in North America, Europe, and Australia- which covers a lot of the world.
Though recessive diseases are more harmful than dominant disorders, they are still present in the world today. Therefore, one can’t be too hypocritical to point out that all recessive alleles cause diseases because a dominant allele could do so too.
References
National Institute of Neurological Disorders and Stroke. (n.d.). Huntington's Disease. Retrieved from National Institute of Neurological Disorders and Stroke: https://www.ninds.nih.gov/health-information/disorders/huntingtons-disease#toc-what-are-the-latest-updates-on-huntington-s-disease-
National Library of Medicine. (n.d.). Type 2 diabetes. Retrieved from MedlinePlus: https://medlineplus.gov/genetics/condition/type-2-diabetes/
Primary Care Notebook. (2018). Autosomal dominant disorders. Retrieved from Primary Care Notebook: https://primarycarenotebook.com/pages/paediatrics/autosomal-dominant-disorders
Starr, B. (2011). Dominant isn't Always Common. Retrieved from KQED: https://www.kqed.org/quest/19237/dominant-isn%E2%80%99t-always-common#:~:text=This%20isn't%20always%20the,trait%20is%20dominant%20or%20recessive.
University of Utah. (n.d.). What are Dominant and Recessive? Retrieved from Learn.Genetics: https://learn.genetics.utah.edu/content/basics/patterns#:~:text=Dominant%20alleles%20are%20not%20better,protein%20that%20makes%20dark%20pigment. Assessed and Endorsed by the MedReport Medical Review Board
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