A1


Person B has two different alleles for X, as evident by the Southern blot. One of the alleles (lower band) is mutated, and the other is intact (higher band - the same size as for Person A, who serves as a positive control). Nevertheless, the HindIII restriction sites in the mutated allele are not eliminated. The fact that the mutated restriction fragment is smaller suggests that a deletion has occurred in one copy of the gene. The one functioning gene is transcribed (as evident by the Northern blot) and translated (as evident by the Western blot) and apparently produces enough protein to render the person asymptomatic. Continue


Person C has only the smaller version of the gene (as evident by the Southern blot). This gene is not transcribed (negative Northern blot), and consequently it is not translated (negative Western blot). Therefore, Person C displays the symptoms described before. The deletion mutation may involve the gene's promoter, thus allowing no transcription. Continue


Person D has a normal-size copy of the gene (as evident by the Southern blot) but no mRNA (negative northern blot) or protein (negative Western blot). There may be a mutation in the promoter region of the gene (a point mutation or a very short deletion that is not detected by the Southern blot) that prevents transcription, but does not alter the HindIII restriction pattern at the DNA level. Continue


Person E has a normal-size copy of the gene (as evident by the Southern blot) that is transcribed to a transcript of the normal size (examine the Northern blot), and yet no protein is made (examine the Western blot). This suggests the existence of a mutation (a point mutation or a very short deletion mutation) that prevents translation. Two possible explanations for the nature of such a mutation are: A mutation that affects the ribosome binding site and prevents initiation of the translation process. A mutation that introduces a premature stop codon in the mRNA very close to the N-terminal of the protein. Continue


Person F has a normal-size copy of the gene (as evident by the Southern blot), that is transcribed to a transcript of the normal size (examine the Northern blot) and translated to a protein of the normal size (as evident by the Western blot). Nevertheless Person F still displays the metabolic problem. This suggests the existence of a mutation (a point mutation or a very short deletion mutation) that affects the activity of the protein. A possible explanation for the nature of such a mutation may be a mutation that compromises the active site of enzyme Y. Continue