Genetics Flashcards
In which one of the following genetic disorders does the DNA mutation display the most homogeneity?
Huntington’s disease
Adult polycystic kidney disease
β thalassaemia
Cystic fibrosis.
Duchenne muscular dystrophy
Huntington’s disease
Huntington’s Disease is caused by an expansion of the CAG triplet repeat in the HTT gene.
The key aspect of Huntington’s disease is the remarkable homogeneity of the mutation; nearly all cases are due to this specific repeat expansion.
This contrasts with the other disorders listed, which are known for their genetic heterogeneity with a wide array of different mutations causing the disease.
A diagnosis of Duchenne muscular dystrophy (DMD) is suspected and blood is taken for dystrophin gene testing
Which of the following is most likely to be found on testing of the dystrophin gene?
Deletion of several exons.
Deletion of one base pair causing a frameshift.
Duplication of several exons.
Splice-site mutation
Missense mutation
Deletion of several exons.
In the case described, the patient is showing classic signs and symptoms of Duchenne Muscular Dystrophy (DMD), such as delayed motor milestones, muscle weakness, calf hypertrophy, and a markedly elevated creatine kinase level. DMD is a genetic disorder caused by mutations in the dystrophin gene, which is one of the largest genes in the human genome.
Among the options given, deletion of several exons is the most common mutation found in patients with DMD. Approximately 60-65% of DMD cases are due to deletions of one or more exons, which disrupt the reading frame of the dystrophin gene.
Which of the following type of mutation results in a single amino acid change in the gene product?
Missense mutation
Nonsense mutation
Silent mutation
Frame shift mutation
Truncating mutation
Missense mutation.
A Missense Mutation occurs when a change in a single nucleotide results in the substitution of one amino acid for another in the protein. This can affect the protein’s function, depending on where the substitution occurs and how different the substituted amino acid is from the original.
What is a Frame Shift Mutation?
Frame Shift Mutation occurs when nucleotides are added or deleted from the DNA sequence, and the number added or deleted is not a multiple of three.
This shifts the “reading frame” of the genetic code, leading to a completely different translation from the original, and usually results in a nonfunctional protein.
What is a Silent Mutation?
Silent Mutation is a type of mutation that occurs when a nucleotide change does not result in a change in the amino acid sequence of the protein.
It’s called “silent” because it has no effect on the protein’s function.
What is a Nonsense Mutation?
Nonsense Mutation is a mutation that changes a codon that codes for an amino acid into a stop codon, leading to the premature termination of the protein.
This usually results in a truncated, nonfunctional protein.
A certain familial cancer syndrome is due to a heritable mutation in a proto-oncogene.
What would be the most common type of mutation in a family with this syndrome?
Missense mutation
Deletion mutation
Insertion mutation
Nonsense mutation
Splicing mutation.
Missense mutation
Proto-oncogenes are normal genes that, when mutated, become oncogenes – genes that can contribute to cancer development. The mutations in proto-oncogenes that lead to cancer generally result in a gain of function, meaning the mutated gene product (protein) is more active or expressed at higher levels than normal, driving uncontrolled cell growth and division.
A missense mutation results in the substitution of one amino acid for another in the protein which can lead to a change in the protein’s function, often resulting in a gain of function, which is most characteristic of proto-oncogenes when they become oncogenes.
