Question

Bully whippets are homozygous for a deletion of two base pairs in the myostatin gene. This deletion changes an mRNA codon in the middle of the myostatin mRNA from UGU to UGA. Use your knowledge of the genetic code to determine the effect of this mutation on the structure of the resulting protein.

Answer 1

The genetic code is a set of rules that dictates the correspondence between the nucleotide sequence in DNA or mRNA and the amino acid sequence in proteins. Each codon in the mRNA specifies a specific amino acid, and the reading of the codons occurs in sets of three.

In this case, the deletion of two base pairs in the myostatin gene changes an mRNA codon from UGU to UGA. The codon UGU encodes for the amino acid cysteine, while UGA is a stop codon that signals the end of translation. Therefore, the mutation results in a premature termination of translation, leading to the production of a truncated protein that lacks a portion of the myostatin protein's normal sequence.

Since myostatin is a negative regulator of muscle growth, the mutation in the bully whippets leads to a loss of function of the myostatin protein, resulting in increased muscle mass and the "bully" phenotype observed in these dogs.

Answer 2

Step-by-step explanation:

The deletion of two base pairs in the myostatin gene in bully whippets results in a frameshift mutation. This means that the reading frame of the mRNA is shifted, causing all subsequent codons to be read incorrectly. The mutation changes an mRNA codon in the middle of the myostatin mRNA from UGU to UGA, which is a stop codon.

UGU normally codes for the amino acid cysteine, but UGA does not code for any amino acid. Instead, it signals the end of the protein chain. Therefore, the mutation results in premature termination of the myostatin protein synthesis.

The resulting protein will be truncated and incomplete, lacking the C-terminal portion of the myostatin protein. This deletion is likely to affect the function of the myostatin protein, which is a negative regulator of muscle growth. As a result, bully whippets have increased muscle mass and strength compared to other whippet breeds.