DNA Day experts answer your questions about types of mutation

18 April 2013

Above: Image © Public Domain, Wikimedia Commons

Which one causes the most harm to a cell, substitution mutation or frame shift mutation?

They can cause harm equally, it just depends on where the mutation in the DNA occurs. For example of a frameshift mutation does not interfere with the normal expression of a gene (so it is a null mutation) there will be no problem but if the mutation causes the expression of that gene to be altered then it can be a problem. Sometimes if the substitution is with a base that represents the same codon for an animo acid, then there is no resulting protein change. Remember there is redundancy in the genetic code, so sometimes a base substitution can result in the same amino acid being used, so it really depends on where the mutation occurs.

- Answer provided by Dr. Dennis McCormac

Which type of mutation would be least harmful to an organism: silent, missense, or nonsense? Would errors in transcription be more or less damaging than errors in DNA replication?

The least harmful of the three mutations is likely silent, as they do not affect the amino acid sequencing of the resulting protein. And I would think that errors in DNA replication may be, on average, more "damaging" as they have the potential to be propagated into all of the daughter cells through mitosis, whereas a single error in transcription would be a one time event.

- Answer provided by Dr. Sean Myles

If we are products of positive mutations, what is an example of negative mutations?

Well, I suppose we are products of both positive and negative mutations. Negative mutations would include disease causing mutations, such as the deletion in the chloride channel that causes cystic fibrosis.

- Answer provided by Dr. Karen Bedard

Are genetic mutations, like nondisjunction, hereditary?

Yes, genetic mutations are generally inheritable, assuming that the offspring survives to adulthood and is fertile. In the specific case of non-disjunction though, the answer for humans is (usually) "no". Nondisjunction leads to extra or missing copies of chromosomes in a fetus, and most of these anomalies lead to spontaneous abortion, stillbirth or early childhood deaths usually. The primary exceptions are Down's Syndrome (extra chromosome 21) Klinefelter's Syndrome (extra X chromosome in a male) and Turner syndrome (missing an X chromosome in a female) where survival into adulthood in normal. In terms of heritability, only 5% of Down's Syndrome patients are explainable by what's called "familial risk" (i.e. something in the family's DNA makeup makes disjunction more likely). Disjunction is well tolerated by plants, and is a way that desirable traits are amplified in plants.

- Answer provided by Dr. Paul Gordon


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