Are physical and/or mental defects caused by the environmental substances that impact the developing fetus like certain drugs or alcohol etc heritable at all? For example if a woman born with fetal alcohol syndrome has a child (with a standard no drinking no drugs pregnancy), is that child at any higher risk for FAS related birth defects due to her FAS birth defects.
I guess I’m asking if birth defect is the result of an environmental aggressor or poison is that birth defect locked in your genes for ever after or not?
Big question, but I would think generally no. FAS specifically, looks like it’s a special case of alcohol poisoning/overdose affecting the developing nervous system of the unborn baby. Has no effect on anybody’s genetics. Under the circumstances you describe I would think the risk for any kind of FAS to her own child would be near zero.
If the environmental substance is a mutagen, however, a substance that does affect genes, then the children of a person exposed in utero could indeed have birth defects. In fact, I believe that the effect would be stronger, or different, for the child conceived and born long after the exposure, because of the way mutagens work individually on different cells in the body.
Generally, that is, mutagens tend to have a somewhat random effect on each cell that they affect. For an adult, this means that any one mutant cell will probably not reproduce to much of their body unless it’s mutated in such a way that its replication controls turn off - a cancer cell. They might get a large number of their cells mutated in different ways or dying off because their mutant nature is not survivable - radiation sickness is the term for this if the mutagen is radiative, I’m not sure if there’s an equivalent for other mutagens.
For an embryo, each mutated cell will probably divide much more because every cell in a developing embryo replicates many many times before the individual is adult. However, a child conceived after mutagen exposure would either be unaffected, or have one side of their DNA entirely derived from a mutant cell in the parent’s gonads, and thus be entirely mutant.
If the mutagen affected the cells that go on to form the gonads in the developing fetus, then it is possible that the mutation could be heritable.
Also, there is the possibility of what are called epigenetic changes. These are changes to DNA caused by external factors. These changes do not change the DNA sequences, but introduce changes to the DNA backbone, and interfere with gene expression. Some of these changes appear to be passed on to offspring, as discussed in a recent New Scientist article. I have a subscription, so will add some quotes, but you may wish to see if you can get the article from a library.
It’s just a flavour from the article (not wanting to quote too much), but it seems clear that environmental factors influencing gene expression may have consequences for offspring (and possibly their offspring). Of course, it is New Scientist and they may be overstating the case, so YMMV.
But it looks like some environmental impacts can influence future offspring.
The thalidomide babies of the late 50’s/early 60’s have an rate of passing on the disabilities 5 times greater than the general population. thalidomide