and again the question stem makes it look like a gene.he CFTR gene is found on an autosome. The most common mutation of the CFTR protein (ΔF508)
Second, the Question stem says that G542X is another allele of the same gene, so that would put G542X and CFTR in the same locus (assuming that CFTR is a gene). The this is what gets confusing because then they are saying that a person can be Aa and the mate can be Bb so what would be the result of that or in this case they are saying one person is G542X -/+ while the other person if CFTR+/- and that makes no sense to me in terms of what cross can happen there. Now at the end of the Question stem they say so assume that none of the parents suffer the disease which clues me that you could infer the other pair for each allele on each parent so the parent that has G542X -/+ would have a mate that is G542X -/- and CFTR +/-. the former in terms will be G542X-/+ and CFTR -/-.
overall my confusion arises from the fact that I don't understand how two different alleles are express for the same gene ( Aa X Bb)