Misconceptions from Mendel


Lately, there has been some controversy about "home genetic testing kits" - which aren't really home testing kits, since you have to mail your saliva out for someone else (presumably NOT in your home) to actually test...but that's not the controversial part.

The FDA has stepped in to prevent the sale of these kits at places like Walgreen's, largely out of fears that people would misinterpret the results. While I feel that people have a right to this information if they want it, the FDA should indeed be concerned about misinterpretation of results.

I think many of these misinterpretations might arise out of misunderstanding the concept of "increased risk," and misconceptions from lessons about Mendel's peas in high school biology. The problem is that many of us don't learn much more about genetics - and forget that we are not peas in a pod. We are people!  And (most) people - as well how their genes influence disease - are more complex than peas.

  • Misconception 1: The path from genotype (genetic makeup) to phenotype (observable characteristics) is deterministic. Mendel's "heritable factors" were rather deterministic in which trait was exhibited.  In most cases, however, the connection from genes/mutations to human disease is not so deterministic.  For example, people discovering they have the BRCA1 mutation might worry that they will definitely get breast cancer.  However, having a disease-associated genotype is not deterministic; rather, it predisposes or increases risk for developing that condition.
  • Misconception 2: Traits are the product of a single gene. Mendel got lucky that the pea traits he studied tended to be single-gene traits.  Most human traits, especially those related to disease, are the product of the influence of many genes and their interaction with the environment, however.  I wouldn't be surprised if Mendel looked at traits such as these, but was unable to make sense of these "non-Mendelian" traits.  Be easy on him though - Mendel was the first one to figure out any of this "genetics" stuff.
  • Misconception 3: There are only two possible variations of a gene. When you're a pea, you can only be green or yellow - seemingly, you get either the green allele or the yellow allele.  But since a mutation can occur at any base pair of the DNA, there are more than just two variations of a gene. Oftentimes, it turns out that there are only a subset of DNA sites that actually demonstrate variation, however, and even fewer of them have any actual effect on the function of the gene product...
  • Misconception 4: All mutations cause strong phenotypic differences. High-school biology Mendel lessons focus on deterministic single-gene alleles producing one of two very distinct phenotypes. Certainly, not all pea genes are like that, but it's hard to notice more subtle characteristics of peas. Peas can't be slightly more outgoing (if they were, I suggest not eating those peas) or have a slightly higher rate of dopamine firing. But words like "predispose" and "increased risk" imply that many mutations have subtle effects that contribute to - but don't determine - the development of certain medical conditions.

Remember, Mendel knew nothing about DNA, just that there were heritable factors - whatever they were - whose influence on physical traits obeyed some simple rules.  We now know much more about genetics and DNA, and people need to become educated on these topics to correctly interpret the results of genetic testing.

My recommendation for the policy side of this: When you "submit your spit" (a catchy slogan?) to the testing kit company, you must designate an independent genetic counselor to receive both your raw data and the company's "risk assessment report."  You must then schedule an appointment with this counselor, who will help you interpret the results.  Furthermore, a number of privacy safeguards must be put in place, since genetic data carries with it a plethora of privacy concerns...



Forcing consumers to use genetic counsellors to access their own genetic data is both paternalistic and impractical. People should be encouraged to seek professional support if they want it, of course, but the idea that I should be MADE to sit down with a counsellor to look at my own genome is ridiculous. In addition, there's simply not enough trained genetic counsellors for this plan be feasible.

GCs will play a vital role in the genomic era for people who do have serious genetic problems - but that doesn't mean they should become the gate-keepers of all genetic information.

Great article - Peter S Harper's book "Practical Genetic Counselling" has a small section about communicating risk, and how most people do not understand what constitutes a high or a low risk, or the scientific reality of genetic contribution to a common disease - hence the need for the genetic counsellor.

In the US if you're uninsured, a genetic counsellor is expensive (see 23andMe's latest genetic counselling service through the "independent" company InformedDNA where counselling is $375 a pop by telephone). Here in the UK genetic counsellors are hard to come by, even on the NHS' regional genetics service, and most of them are trained in monogenetic disorders. What generally happens is a consumer purchases a DNA profile from 23andMe, they get scared because they think their going to die from 50 different diseases and then run to a GP who knows even less about it than they do!

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