2012 National DNA Day Online Chatroom Transcript
This is just one question from an archive of the National DNA Day Moderated Chat held in April 2012. The NHGRI Director and many genomics experts from across NHGRI took questions from students, teachers and the general public on topics ranging from basic genomic research, to the genetic basis of disease, to ethical questions about genetic privacy.
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Why can a genetic defect appear in generation but skip the next generation and then reappear in a diffrent generation?
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Brandon Colby:
I am the author of the book "Outsmart Your Genes", which discusses genetic testing and the personal genomics revolution. I am also the CEO & Medical Director of Existence Genetics, a company that provides comprehensive genetic testing services to healthcare professionals. I practice Predictive Medicine in Los Angeles, California.
A genetic trait or disorder can appear to 'skip' a generation, only to reappear in a future generation, for many different reasons. One reason is that the gene that determines this trait or disorder may appear on the 'X-chromosome'. Since men only have one X-chromosome, if there is a genetic mutation on the X-chromosome in a man then he may have a specific trait or disorder. Then if that man has a daughter, she will have two X-chromosomes (since females have two X-chromosomes) - one she inherited from her father, that will have the mutation, and one she inherited from her mother, who does NOT have the mutation. The X-chromosome that does not have the mutation may then cause the daughter to not have the trait or disorder. If that daughter then grows up and has a son, that son has a 50% chance of inheriting the X-chromosome without the mutation and a 50% chance of inherited the X-chromosome with the mutation, which means that son will have a 50% chance of having the trait or disorder, just like his grandfather did. Thus, it would appear that the trait or disorder "skipped" a generation and went from grandfather to grandson. |
| Peru High School in IN (9th grade student) |
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