DNA Day experts answer your questions about genetic disorders

Above: Image © RKaulitzki, iStockphoto.com

Are recessive genetic disorders more common than dominant ones?

Hmmm, a surprisingly thought provoking question, thanks! I just did a quick search of one of the major genetic disease databases (OMIM), and there are about 1.5 recessive disease genes for every 1 dominant. That doesn't say anything about prevalence of the disorders they cause though. I'm not trying to cop out of your question, but I guess the answer depends a bit on how you want to define "disorder"� Suppose we're talking about severe, debilitating disease caused by one simple gene mutation. The most common causes of these are either recessive (both parents are unaffected disease carriers) or new mutations in the child ("de novo dominant"). This is because affected individuals are less likely to have their own offspring and put these variants into the gene pool. If instead we talk about disorders that do not greatly affect reproduction rates, such as arthritis or Alzheimer's, it's quite possible that the underlying genetic causes are either dominant, or involve multiple genes (a type of recessiveness in the broader sense). For disorders in between these two extremes (e.g. congenital heart disease, intellectual disability), we've definitely a significant mix of both recessive and dominant.

- Answer provided by Dr. Paul Gordon

How are generic disorders recognized by using a karyotype chart?

Not all can be, but any disorder that is caused by missing chromosomes, duplicate chromosomes, or rearrangement of sections of a chromosome (like a piece that has been detached, turned around and re-attached) can literally be seen. More subtle things, like a single nucleotide substitution for instance, cannot be identified this way.

- Answer provided by Jay Ingram

With technology improving every day, will it ever be possible to reverse or modify genetic conditions?

I believe so. In particular for conditions where a mutation leads to a very tissue specific defect, like for example the eye - researchers are getting very close to being able to deliver a DNA to replace the defective gene in such cases. It will be more challenging for situations where the gene is needed in every part of the body, but these are still early days.

- Answer provided by Dr. Karen Bedard

Are there certain genes that can increase the chances of mental disorders such as OCD, depression or anxiety?

Genes that increase the chances of mental disorders? There are forms of genes - alleles - that do. We don't know what they are, but that is one of the things that genetics is working on. We all basically have the same set of genes - what differs from one person to the next are the forms - the alleles. Think brown eyes/blue eyes. In this way, there are alleles for genes that do influence the chances of having almost any disease, including mental illness.

- Answer provided by Dr. Thomas Merritt


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