Genetics

A couple seeks your advice regarding the recurrence risk of the NARP (neuropathy, ataxia, retinitis pigmentosa) syndrome, a disorder with mitochondrial inheritance. They are first cousins and have a family history of the condition.

What is the impact of their consanguinity on the risk of having an affected child?

In which one of the following genetic disorders does the DNA mutation display the most homogeneity?

The mutation in the haemochromatosis (HFE) gene is present in approximately 10% of the Caucasian population. The diagram below shows that three men in a family have been diagnosed with haemochromatosis.

What is the risk that the woman (indicated by the arrow in the pedigree below) has inherited the genetic predisposition to develop this disorder?

A teenager is evaluated because of delayed motor milestones. On examination he has muscle weakness with calf hypertrophy. He has a markedly elevated creatine kinase level of 15,400 I/U [<240 I/U].

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?

Which of the following type of mutation results in a single amino acid change in the gene product?

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?

What is the most likely effect at the protein level of a 1 base pair deletion within an exon of a gene?

A patient has haemophilia A due to a frameshift mutation in the F8C gene. At the conclusion of the S-phase in a cell of this patient, how many copies of the F8C gene would be present in the cell?

A patient with a mitochondrial cytopathy is found to have a frameshift mutation in the ND4 gene, a complex I gene in the mitochondrial genome.

Which of the following statements represents the most likely outcome of this mutation?

Different mutations in the DMD (Duchenne muscular dystrophy) gene cause three clinically distinct syndromes in males. The table below lists the three conditions, the degree of skeletal muscle weakness, and a number of different abnormal genotypes involving the DMD gene.

Which of the following represents the most likely relationship between the genotypes and phenotypes?

A frameshift mutation is best described as a:

In a family in which two boys are affected by an X-linked disorder, a causative point mutation is identified. On blood testing, the mutation is found in both boys but not demonstrated in the mother.

The most likely explanation for this finding is:

A woman presents for genetic counselling early in her first pregnancy. Her husband has a disorder caused by a mitochondrial DNA point mutation; several other members of his family are also affected.

The risk that this baby will be affected by the same condition is closest to:

Which one of the following types of mutation is most likely to lead to the introduction of a premature stop codon?

In the pedigree shown, individuals marked with an X have a rare genetic disorder. Those marked with an N are clinically normal. Those with a slash are deceased and the remaining family members have not been examined clinically.

From the pedigree which one of the following is the most likely mode of genetic inheritance?

A non-consanguineous family with a rare genetic disease has been identified. The pedigree is shown below.

What is the most likely mode of inheritance?

A 16-year-old boy (indicated by the arrow in the pedigree below) has been diagnosed with myotonic dystrophy. The diagnosis is confirmed by DNA testing. His mother’s cousin has myotonic dystrophy, but the other surviving relatives have no history suggestive of a myopathy.

What is the most likely explanation for this pedigree?

In a study of polymorphisms in the gene encoding the β2-adrenergic receptor, 20% of people were heterozygous for a polymorphism at codon 16 and 22% were heterozygous for a polymorphism at codon 27. 18% of the population were heterozygous at both loci.

Which one of the following statements is the best explanation for this observation?

A number of members of a family are affected with a rare syndrome of external ophthalmoplegia, Parkinsonism, and early menopause. DNA studies identified multiple deletions of various sizes in mitochondrial DNA in the affected people. The pedigree is shown below.

What is the most likely mode of inheritance of this syndrome?

X-linked dominant inheritance is distinguished by:

What is the most likely inheritance pattern in this family?

The normal phenotype of individual II:3 in the family below is best explained by: