Common Misconceptions About Genetics

Seven decades have passed since scientists proved that DNA is the cornerstone of heredity. Since then, a plethora of new DNA tests, as well as a steady stream of books, news programs, and CSI episodes, have made us comfortable with the idea that each of our cells incorporates three billion base pairs of DNA that we inherited from our parents. These test results can teach us a lot about ourselves. However, there is a significant risk of drawing incorrect conclusions.

Because of the availability of a wide variety of genetic tests, scientists today are sending out warnings around what they call “genetic astrology.” While genetics and our DNA remain fascinating, it is important to be aware of the facts. Such as…

10. Traits are solely determined by genes


Although some traits, such as blood type, are solely decided by genetics, the majority of traits are strongly affected by both genes and the environment in general. We do not inherit diseases; rather, we inherit predisposing factors that influence our risk of developing a disease. Recent research, for example, suggests that 50-60% of the risk of alcoholism is genetic. This means that the remaining 40 to 50 percent of the risk is environmental in nature. Because of a family history of alcoholism, a person may be genetically predisposed to it. However, certain healthy lifestyle choices, such as limiting alcohol consumption, can help prevent that person from ever becoming addicted to alcohol.

For people who are predisposed to obesity, a positive environment can have the same effect. Obesity has a hereditary component that is influenced by a number of genes. However, research on the degree of genetic input has produced wildly disparate results. Obesity can run in families, but if an individual chooses to eat healthily and exercise consistently, he or she can avoid it.

9. The majority of traits are provided by single genes


Most human features, such as height, eye color, and skin color, are determined by multiple genes rather than a single gene. When a trait is regulated by multiple genes it is called polygenic. Multiple genes code for the same trait, therefore there are no distinct classes; instead, there is a range, which is why there can be such wide variances when it comes to skin color or height. Even eye color varies from brown to blue to green to hazel or beautiful shades in-between colors.

According to recent findings, nearly 100 genes play a role in and can influence our skin color. We all, for example, have a number of genes involved in the creation of melanin (the substance that is responsible for our skin color). Nevertheless, we all differ when it comes to the amount and the type of melanin we produce – which can range from brown to reddish to black. Many of us were also taught in high school that brown hair is more dominant than blond hair. This lesson was frequently supplemented by a Punnett square that focussed on single gene equations.  Today we know that pigmentation inheritance is in fact much more complicated and therefore can’t be explained by a basic single-gene equation.

8. Dominant traits are the traits that are most prevalent in a population


When we hear the term “dominant,” we frequently assume that this trait or characteristic is shared by the majority of the population. However, when a trait is described as dominant, it does not imply that it is the most prevalent; rather, it indicates that it is exhibited over the recessive trait. Tongue rolling, for example, is a dominant trait governed by the dominant variant of a gene. Tongue rolling is seen in people who have one or two copies of the dominant variation. Only people with two recessive variants of this specific gene will be unable to roll their tongues.

Similarly, whether a trait is recessive or dominant has nothing to do with its frequency of recognition in a community or demographic. Instead, it reflects how frequently the genes responsible for a particular characteristic or trait are found in individuals. A dominant mutation can also cause polydactyly or the presence of extra fingers and/or toes. Polydactyly, on the other hand, occurs in approximately 0.30-6.00 births per 1,000 and is more closely related to a person’s ethnic background. This means that, while the polydactyly-causing gene mutation is dominant, it is extremely rare for a person to have it.

7. The intricacy of genome sequencing is a barrier to obtaining genetic information

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Thanks to technological advances, the human genome can now be sequenced fairly quickly and easily. It wasn’t always this simple. It took the “Human Genome Project” over 12 years and approximately $2.7 billion to sequence the first human genome. For less than $10,000, the human genome can now be sequenced in a matter of days. The ability to obtain genetic information is no longer constrained by time or cost. In all honesty, now that we have the data, the most difficult part is analyzing the genome, which can remain a challenge for a little bit longer.

Sequence data consists of a very long string of the letters A, T, G, and C, that correlate to the basic components or building blocks of our DNA. Bioinformaticists are the scientists who specialize in analyzing this data. They make use of software applications to determine which genetic traits are linked to specific genes and how the genes interact with and ultimately influence one another. Scientists believe that the roles of all  22,000 genes in the human genome will eventually be identified and understood.

6. All genetic mutations are dangerous


The majority of mutations in our DNA sequence are single nucleotide changes that are not dangerous at all. According to new findings, everyone inherits up to 60 new mutations that can not be found in our parents. Some of these mutations account for the .1% difference in the genomes of any two people. Occasionally mutations also occur in places that play no role in our genes, therefore the person remains unchanged. When mutations arise in a gene, the protein encoded by that gene may or may not change significantly. The mutation is also very likely to go unnoticed.

Mutations can even be beneficial to a person. A mutation, for example, could result in a gene that confers resistance to infections and even serious diseases. Individuals who carry the mutation will survive illnesses and eventually pass it on to their children. CCR5 is a good example of a mutation. If not treated, the HIV virus clings to CCR5 as a mechanism to infect a cell, eventually leading to AIDS. However, approximately 10% of people of European ancestry have a deletion in their CCR5 gene. This mutation prevents the HIV virus from binding effectively to a host cell, resulting in a delay in virus’ entry and a lower risk of developing AIDS.

5. It is possible to “fix” a mutation once it has been identified


Once a mutation has taken place in the genome, it cannot be reversed or “fixed.” Instead, scientists daily look at ways to develop or identify drugs or other treatments to counter faulty genes and disease-causing mutations since the technology to fix DNA errors doesn’t exist yet. Huntington’s disease is an amazing example of this type of mutation. Huntington’s disease is caused by an incorrect replication of the nucleotide CAG within the huntingtin gene. To date, Huntington’s disease has no cure – despite the fact that we know exactly what causes it.

Ongoing research in the area of gene therapy, an experimental technique for treating and preventing illnesses shows a lot of promise. Rather than utilizing drugs or surgical procedures to treat a patient’s illness, this technology may allow doctors to treat disorders by transferring correcting genes into the patient’s cells. The majority of studies to date have been done on mice, but scientists intend to refine this technique in the future so that it can be used to treat a wide range of diseases.

4. Every genetic test is equally accurate and dependable

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All of the genetic tests available today are not equal in accuracy and reliability. Any time you’re considering genetic testing, it’s important to have a clear idea of what you’d like the test to reveal and to thoroughly investigate the test that will deliver the most accurate results. Some tests, such as presymptomatic testing for Huntington’s disease, produce 100% definite results. While others may only provide you with your average percentage risk when stating your predisposition for a specific illness. 

For example, genetic test results may reveal that you have an 18% chance of developing a particular disease. This result will be worrying at first, after further investigation, you might find that the public, in general, has a 15% chance of contracting the same disease. This means that, while your risk is higher than normal, it is not high enough to justify drastic changes in your lifestyle to avoid contracting the illness. When your test results highlight any specific predisposition to a particular disease it does not necessarily mean that you will develop the disease in the future; it merely shows that you have a higher likelihood of getting it.

3. “Disease genes” are very rare


Genetic diseases are associated with mutations in the genes that everyone has. For instance, most of us have heard about the “breast cancer gene,” BRCA1. What you may or may not know, is that both men and women have the BRCA1 gene. BRCA1’s everyday function is to generate a protein that aids in the repair of DNA damage. If you have a version of BRCA1 that does not function correctly you are more likely to accumulate DNA damage. This damage has the potential to eventually cause cancer.

Every woman has a 12% chance of developing breast cancer during her lifetime. However, women with the mutated BRCA1 or BRCA2 gene’s risk of developing breast cancer is between 69% and 72% – that’s 6 times higher than without the mutation. A woman with the mutated gene’s risk of developing ovarian cancer also rises significantly – between 17% and 44% compared to a mere 2% in the overall population. Unfortunately, men with the BRCA mutations are just as likely to develop breast cancer during their lifetime, particularly if the BRCA2 gene is mutated. According to one study, men with a BRCA2 mutation have an 8% lifetime risk of developing breast cancer. These men are also more prone to developing prostate cancer.

2. If there’s a “1-in-4” chance of having a child with a genetic disease, the risk profile changes after the first child is born


A “one-in-four” risk doesn’t really imply that one out of every four children born to a couple will be affected by a particular illness. Instead, the  “one-in-four” risk indicates that every child has a 25% (or one in four) chance of ultimately having the disease. A Punnett square will quite often correctly depict the likelihood of the children’s inheritance. For example, suppose a married couple is both carriers of sickle cell anemia, it would make them heterozygous, as they both have one dominant and one recessive allele (Ss). 

In this example, any children born from their relationship would have a 50% chance of being heterozygous (Ss), a 25% chance of being homozygous recessive (ss), and a 25% chance of being homozygous dominant (SS). Because sickle cell anemia is a recessive disease, it affects only homozygous recessive children. It is worth noting that just because one child has the disorder, it does not actually imply that future offspring of the same couple will be less likely to inherit the disorder. Unfortunately, all of the couple’s children will have the same chance of inheriting the disease.

1. In agriculture, genes are only found in genetically modified crops


Genes can be found in all agricultural crops, whether or not they have been genetically altered. Like humans, plants have DNA that decides which phenotypic traits will appear based on the genotypes of the plant. Gregor Mendel, the father of genetics, actually discovered how genes behave while examining pea plants. Agricultural crops that have been genetically manipulated diverge from traditional food crops as genes from other organisms have been embedded into their genetic code. The most widespread modifications are bacteria-derived genes used to make crops resistant to pesticides and herbicides.

This enables farmers to spray herbicides on their fields to control weeds without negatively impacting the crops, or to use fewer pesticides because the crops are already pest resistant. As a result, the only genetic distinction between GMO crops and conventional crops is the addition of one or two genes. GMO plants and crops remain a hot topic. There has been much debate about the labeling of foods containing GMO plant products and hundreds of organizations worldwide continue to fight against its use.

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