Mock 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?

No alteration to risk.

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Approximately 10% reduction in risk.

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Approximately 10% increase in risk.

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Approximately 25% increase in risk.

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The alteration in risk can only be determined by a detailed examination of the pedigree.

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

Huntington's disease

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Adult polycystic kidney disease

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β thalassaemia

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Cystic fibrosis.

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Duchenne muscular dystrophy

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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?

5%.

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<1%.

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10%.

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25%.

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50%.

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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?

Deletion of several exons.

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Deletion of one base pair causing a frameshift.

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Duplication of several exons.

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Missense mutation

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Splice-site mutation

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

Missense mutation

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Frame shift mutation

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Nonsense mutation

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Silent mutation

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Truncating mutation

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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

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Deletion mutation

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Insertion mutation

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Nonsense mutation

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Splicing mutation.

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

Frameshift resulting in abnormal protein sequence from the site of the deletion.

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No effect (i.e. benign polymorphism).

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Premature stop codon at the site of the deletion resulting in a prematurely truncated protein (nonsense mutation).

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Single amino acid (missense) change.

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Splicing abnormality resulting in exon skipping.

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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?

2 cells

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0 cells

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1 cells

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3 cells

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4 cells

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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?

Heteroplasmy with mitochondrial inheritance.

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Polyplasmy with expression limited to females.

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Homoplasmy with autosomal recessive inheritance.

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Heteroplasmy with autosomal recessive inheritance.

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Homoplasmy with mitochondrial inheritance.

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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?

Option B

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Option A

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Option C

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Option D

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Option E

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A frameshift mutation is best described as a:

mutation which alters the codons downstream of its location

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missing base or set of bases which results in a premature stop codon.

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mutation which alters the normal splicing of an intron.

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sequence alteration which occurs at or near regulatory sequences in the 5' untranslated region of the gene.

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single base change which alters that codon to one which now reads stop.

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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:

maternal gonadal mosaicism for the mutation.

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laboratory error.

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non-maternity.

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recurrent new mutation

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skewing of X-inactivation in the mother's blood.

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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:

0%

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5%

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25%

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50%

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100%

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

1 base pair insertion in an exon.

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1 base pair insertion in the promoter

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2 base pair duplication in an intron.

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3 base pair deletion in an exon.

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3 base pair inversion in an exon.

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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?

Autosomal dominant

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Autosomal recessive

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X-linked

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Mitochondrial.

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Epigenetic

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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?

Autosomal dominant.

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Mitochondrial.

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X-linked

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Autosomal recessive.

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Polygenic.

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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?

Incomplete penetrance.

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Consanguinity.

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Imprinting.

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Non-paternity.

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Mitochondrial inheritance.

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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?

Linkage disequilibrium between the two polymorphisms

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Low frequency of recombination between the two polymorphisms

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Co-inheritance of the two polymorphisms providing a selective advantage.

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Intragenic cross-over between the two codons

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Variable triplet repeat expansion between the two codons.

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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?

Autosomal dominant without imprinting

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Autosomal dominant with maternal imprinting

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Autosomal recessive without imprinting

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Autosomal dominant with paternal imprinting

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Mitochondrial with incomplete penetrance.

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X-linked dominant inheritance is distinguished by:

females often less variable but more severely affected than males

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affected males having affected daughters and healthy sons

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affected females having affected daughters and healthy sons.

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males often being more variably and mildly affected than females.

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healthy females having affected sons and healthy daughters.

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What is the most likely inheritance pattern in this family?

Dominant inheritance with maternal imprinting

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Dominant inheritance with anticipation.

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Dominant inheritance with variable expressivity

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Dominant inheritance with paternal imprinting.

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Dominant inheritance with incomplete penetrance

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

non-penetrance

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maternal imprinting.

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non-paternity

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multigenic inheritance

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X-linked recessive inheritance

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Mock Genetics

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