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You say this is a real life problem. The doctors or counsellors will no doubt want to investigate for information more complete than what we have, they can identify the molecular DNA change that has caused the affliction in the son, then they can establish whether the mother’s sister has that gene damage or not. If you are saying this is Lowe’s syndrome, I see there is a specific known gene involved, all those putatively gas oil ratio for weed eater bearing the mutant gene, the grandmother if alive and other female relatives, can be checked I guess in any reasonably modern health system. If she has it then there is a very great risk for having children. If not I guess there is no more risk than anyone else, however we cannot give medical advice here and this should not be taken as such.

We here do not even know whether the grandmother was a carrier. Since you say there is a 2/3 chance the mother was a carrier by the same token that makes 4/9 chance the grandmother was, hence a 4/18 = 2/9 chance the sister is. High risk. Only other thing we know is the grandmother had one unaffected son; whatever change that makes to the probability I would not place any bets when the stakes are so high.

One can say that it is the nature of severe disease-causing X chromosome mutations that a large fraction of them are de novo. The affected males do not have progeny so there is high selection pressure electricity 2pm mp3 eliminating the mutant genes, therefore a high fraction of the mutations must be recent, either de novo, or a very few generations back. This is also the case for dominant mutations in general, but quite different for recessive autosomal mutations whose origins can often be traced or inferred centuries and even millennia back.

It was not obvious to me until the moment of writing this why the novo fraction is not higher than ⅓ , why it is not ½. Suppose you have a population with some fraction of females with a deleterious de novo mutation gas in babies an X- chromosome gene who each produce two offspring. 1/4 of this offspring are afflicted males who do not produce offspring. An equal number are carrier females. These will in future generations give rise to afflicted males which will count as inherited, not de novo And without so much as summing a series all mutant genes will sooner or later end up this way, so the total number of inherited mutations expressed as disease will be equal to the first generation number. I.e. a 1:1 ratio de novo and inherited X’.

However in that case the whole sub population has halved. Suppose instead their reproduction rate is higher so as to maintain a constant population, i.e. averagely each female instead of two children produces 2×4/3, then they will maintain a constant population and I think I actually produce twice as many as the F1 afflicted males. And an even higher ratioif the population is expanding.

When I hear the term ‘de novo mutation’ this mostly means a mutation that has originated not all that recently in a grandparent of the affected male individual. (More likely grandfather than e payment electricity bill maharashtra grandmother for reasons explained in the reference below.) It is present in one of the chromosomes of the mother Who is consequently a ‘carrier’ but was not present in the somatic chromosomes of her parents nor an ancestor further back.The most easily found online sources and of the elementary textbooks as far as I know strongly emphasise these carrier females, and much less how this mutation comes to be present in them. At some point in the differentiation and proliferation gas explosion of germ cells during development of grandparents the mutation occurs and is present in all the cells that have descended from the mutant one, but not in others. The grandparents are then is said to be mosaics with respect to this type of cell.Then if it is the descendent of one of these mutant cells that happens to end up in the gamete that forms their daughter (the ‘mother’) she will have homogeneously half her chromosomes bearing the mutation and will be what we call the carrier. That seems to be the classical or textbook story.

However it is also possible that this mother who has not inherited a mutation acquires one in her own germ cells which form a mosaic. So with reduced probability this could be transmitted to a daughter – that is just the process we already described – but also to a son.As far as I could make a note from the difficult publication cited below something in the range 4-10% of the de novo mutations found in males are of this kind of origin. Perhaps in earlier years the mosaicism of mothers would not have been detected, but now the techniques are better.

Finally 10 ethanol gas problems the publication points out further that this type of disease can come about via what I think used to be called ‘somatic mutation’ but the publication calls ‘postzygotic de novo .mutation’.Here a mutation has occurred not in the germline of the affected individual, but in some of his somatic cells – He is himself a mosaic with respect to the mutation. close to 7% of seemingly de novo mutations arise as postzygotic events in the offspring. This is a relatively recent biomedical research and discovery theme.