45 B7. The diagram above shows the intron/exon structure of the PHYH gene, encod

Question

45 B7. The diagram above shows the intron/exon structure of the PHYH gene, encoding a protein called phytanoyl- CoA 2-hydrolase. The protein is responsible for disposing of phytanic acid taken in through the diet. The exons are numbered and the intron lengths shown below the thin lines. The shaded regions correspond to the ORF. The symbols at the top of the diagram indicate some of the mutations in this gene that have been found in human populations. In this system of nomenclature, the 85C>T (for example) means that the normal C at position 85 is a T in the mutant allele. (Ignore the ones that deal with the introns, e.g, IVS2, etc). Ins means insertion and del means deletion. In principle, some of these mutations could lead to the occurrence of in-frame stop codons, whereas others cannot do so. Please list TWO mutations that could potentially produce stop codons and TWO that cannot, explaining why in each case B8. Please choose from the following list to fill in the blanks below. Each question has ONE answer, and eacl answer should be used only once. Alpha satellite, promoter, c, 2c, 4c, n, 2n, 4n, STR locus, LI (line), 5 UTR, GUIAG splice junction, polyA tail UTR, AUG start codon, triploidy, trisomy monosomy, translocation, PKU, CF, tyrosinemia, alkaptonuria, Tay-Sachs disease, ASO, dot blot, reverse dot blot, nonsense, missense, silent

Explanation / Answer

1. 85 C->T

In this case, C is changing into T. Both C and T are purines. So, there be not enough change in the DNA codon. This is a case of point mutation.

2. 517 C->T

In this case, C is changing into T. Both C and T are purines. So, there be not enough change in the DNA codon. This is a case of point mutation.

Two mutation that could produce stop codon are:

1. 164delT

In this case, Thymine is deleted from the sequence of DNA , which could change the reading frame of the sequence and hence, could lead to the production of stop codons.

2. 576-577insGCC

In this case, codon GCC has added , which could change the reading frame of the sequence and hence, could lead to the production of stop codons

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