Question

Helen has type I osteogenesis imperfecta (Oi), a genetic skeletal disorder. Shown below is her DNA sequence for a portion of the coding region of the collagen type I gene, which contains the mutation responsible for her disorder. The corresponding wild-type sequence is shown also (only one DNA strand is shown in each case). Helen Normal 5-AAACTCCACTTCTTCCAGTAC-3' 5'-AAACTCACTTCTTCCAGTAC-3' What type of mutation does Helen carry? frameshift-deletion frameshift-insertion nonsense silent missense
help please as soon as possible

Answer 1

Helen carry frameshift-insertion mutation.

Because extra one base (cytosine : C) is added at the 7th position of Helen's DNA sequence for a portion of the coding region of the collagen type 1 gene . As a result, due to insertion of a base, triplet codon sequence is changed, reading frame is also changed, completely different protein is formed from normal peptide sequence and it caused frameshift-insertion mutation and it is responsible for her skeletal disorder. Frameshift mutation can be caused by addition or deletion of a nucleotide base in DNA sequence.

It is not Frameshift deletion mutation because here no base is deleted from normal gene sequence rather one base is added. This mutation is not nonsense mutation because mutated codon is not a STOP codon. It is not silent mutation because amino acids of a newly generated peptide sequence of mutated region is not similar to unmutated amino acids sequence, rather it's completely different protein and observable phenotypic effect (OI disorder) is found due to mutation which is mentioned in the following image. It is not a missense mutation also because no single nucleotide is changed in Helen's DNA sequence compared to original DNA sequence.

All details are given in the following image.

onobose is This base is inserted kextramt Coding strand Helen 5 AAACTERACTT CT T C CAGTAC-3 Nosomal 5-AAACTS ACTTCTICLAGTAC-3 Helen 5'- AAA CUCCACUULUUC CAGUAR-3' transcripted Normal 5-AAACUE ACUUCUU CCA GUAC-3 RNA peptide Как ИХ Helen lys-leu-his- phe-phe-gln-tyro . Normal lys- lel-the-ser-ser-sert Due to insertion of cytosine, codon is shifted therefore completely different peptide sequence is generated 'which is non frictional compared to Normal gene sequence , so the mutationis Franceskatt minta nation and Helen enrry it that's why she has Type I Osteogenesis muporfecta (07), genetic disonder