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Name: Diane P.
Status: Educator
Age: 50s
Location: N/A
Country: N/A
Date: August 2004


Question:
Is it possible to identify a defective gene in an unfertilized egg without destroying the egg? (Making it possible to then select an egg without a defective gene for in vitro fertilization.)



Replies:
Interesting question...Not directly to my knowledge, but cytogenticists can use "genetic probes" karyotypes and various advanced tests on the person's non sex cells (such as white blood cells) that are not the egg cell and find out if they posess chromosomes that contain certain genetic anomalies that would be passed on into the egg cells of that person. This would predict if a certain person would pass on certain genetic problems through their egg cells but NOT any one specific egg since any certain egg cell might have had an error in its genetic compliment when it was produced in meiosis in addition to any genetic anomalies it inherently had. So the indirect answer is yes... but not by doing tests on the egg itself. Furthermore, genetic tests could reasonably rule out certain genetic defects but would not guarantee that the egg was free of genetic defects.

pf


No. As the student suggested, analysis of the ovum's DNA would entail destructive testing of the DNA.

Ron Baker, Ph.D.


Dear Diane P.,

As far as I am aware, there is no technology that can identify defective genes within an egg without destroying it or potentially interfering with the developmental potential of the egg. Using the principles of genetics, we can say that if the defective gene is present in a homozygous condition (two copies of the defective gene), the egg will certainly have it. However, if only one of the two copies is defective, we can predict statistically the chances of the egg bearing the defective gene, but for an individual egg we cannot. The one exception would be if the defective gene has some effect on the egg that could be distinguished from a normal egg. A non-egg example would be sperm where there are physiological differences between sperm carrying the X or Y chromosomes that can be exploited to enrich for one or the other type. (I leave it to you whether you would consider one of those chromosomes to be defective!)

Thus the challenges will be to find a noninterfering way to identify defective genes or to identify nonDNA-based methods for distinguishing individual products or consequences of a defective gene in the egg.

Thanks for the question.

Jim Tokuhisa



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