KMU Past Paper Practice

Question:

A child has a pathogenic DNA variant identified on genetic testing. The physician explains that the laboratory finding represents the child’s genetic constitution, while the clinical manifestations are its observable expression. Which term specifically refers to the genetic constitution?

Options:

Correct Answer: Genotype

Explanation: Genotype describes an individual’s genetic constitution, whereas phenotype represents the observable expression produced by that genetic background and other modifying influences.

Question:

During analysis of a mutant gene, a nucleotide change is found at the boundary between an exon and an intron. The coding sequence itself is largely preserved, but the mature messenger RNA is abnormal. Which process has most likely been disturbed?

Options:

Correct Answer: RNA splicing

Explanation: Mutations at splice sites can interfere with normal removal of introns and joining of exons, producing an abnormal mature mRNA and consequently an abnormal gene product.

Question:

A mutation increases the activity of a regulatory protein rather than reducing its production. A single mutant allele produces the clinical phenotype. Which molecular mechanism best accounts for this form of dominant disease?

Options:

Correct Answer: Gain of function

Explanation: A gain-of-function mutation gives a protein excessive or abnormal activity. Such mutations can behave dominantly because one abnormal allele is sufficient to alter cellular function.

Question:

A three-nucleotide sequence within a gene is found in many more copies than expected. The abnormal sequence becomes larger during transmission within the family. Which feature of the mutation is most important for development of the disorder?

Options:

Correct Answer: Expansion beyond a critical repeat length

Explanation: Trinucleotide-repeat disorders develop when the repeat expands beyond a critical range, disturbing gene expression or protein function.

Question:

A student is asked to identify another disorder, besides Huntington disease, in which expansion of a three-base DNA repeat is an important genetic mechanism. Which condition is the best answer?

Options:

Correct Answer: Fragile X syndrome

Explanation: Fragile X syndrome is an important trinucleotide-repeat disorder. Myotonic dystrophy and Friedreich ataxia are other examples within this group.

Question:

A woman has a genetically determined disorder affecting oxidative phosphorylation. Her skeletal muscles and nervous system show prominent dysfunction. Why are these tissues particularly vulnerable to this category of mutation?

Options:

Correct Answer: They require substantial cellular energy production

Explanation: Mitochondrial mutations can impair oxidative phosphorylation. High-energy tissues such as nervous tissue and muscle are particularly sensitive to reduced ATP production.

Question:

A pedigree contains affected males and females in three successive generations. An affected woman has affected and unaffected children of both sexes. Which additional finding would most strongly support an autosomal dominant rather than an X-linked pattern?

Options:

Correct Answer: Transmission from father to son

Explanation: Male-to-male transmission establishes that the responsible allele is not being transmitted on the X chromosome and strongly supports an autosomal pattern.

Question:

A child has an inherited lysosomal enzyme deficiency. Microscopy shows progressive accumulation of material inside lysosomes. Which mechanism most directly produces this cellular change?

Options:

Correct Answer: Failure to degrade the enzyme’s substrate

Explanation: Loss of a lysosomal enzyme prevents normal degradation of its substrate, causing progressive intracellular storage of undegraded material.

Question:

A patient has an inherited disorder in which the amount of a normal structural protein produced by one functioning allele is insufficient to maintain normal tissue function. Which molecular principle best describes this situation?

Options:

Correct Answer: Insufficient quantity of normal protein

Explanation: Some dominant disorders occur because a single functioning allele cannot produce enough normal protein to maintain normal cellular or tissue function.

Question:

A patient with an inherited connective-tissue disorder has reduced mechanical integrity of several tissues despite normal metabolic enzyme activity. Which category of gene product is most likely abnormal?

Options:

Correct Answer: Structural non-enzyme protein

Explanation: Mutations affecting structural proteins can weaken tissue architecture even when metabolic enzyme pathways remain intact.

Question:

Two patients receive the same oxidant medication. One develops acute red-cell injury because of an inherited enzyme deficiency, while the other remains unaffected. Which relationship best explains the difference in response?

Options:

Correct Answer: Genetic variation modifies susceptibility to drug toxicity

Explanation: Inherited enzyme abnormalities can make selected individuals unusually susceptible to adverse drug effects, demonstrating the clinical importance of pharmacogenetic variation.

Question:

Several members of a family carry susceptibility variants for a common disease, but only some develop clinical illness after interaction with relevant environmental factors. Which feature most clearly distinguishes this pattern from a classical Mendelian disorder?

Options:

Correct Answer: Contribution from multiple genes and environment

Explanation: Complex multifactorial disorders arise from combined effects of several susceptibility genes and environmental influences rather than a single-gene Mendelian pattern.

Question:

A newborn has generalized hypotonia, a flat facial profile, upslanting palpebral fissures and a congenital cardiac abnormality. The developmental abnormalities are ultimately related to increased expression of genes carried on chromosome 21. Which pathogenic principle best explains these findings?

Options:

Correct Answer: Increased chromosome 21 gene dosage

Explanation: Down syndrome results from excess chromosome 21 genetic material. Increased dosage and expression of genes on chromosome 21 disturb normal development and produce the phenotype.

Question:

An infant has several physical findings suggestive of Down syndrome. The clinician explains to the parents that these findings raise suspicion but do not independently establish the underlying chromosomal abnormality. Which principle is most appropriate?

Options:

Correct Answer: A characteristic combination prompts cytogenetic confirmation

Explanation: A combination of characteristic clinical findings raises suspicion for Down syndrome, but demonstration of the underlying chromosome 21 abnormality confirms the genetic diagnosis.

Question:

A laboratory performs repeated cycles of DNA amplification. Primers have already bound to complementary sequences surrounding the target region. Which event should occur next to generate new copies of the target?

Options:

Correct Answer: DNA polymerase extends the bound primers

Explanation: After primer annealing in PCR, thermostable DNA polymerase extends the primers by synthesizing complementary DNA strands; repeated cycles amplify the target.

Question:

A molecular laboratory wants to determine whether a selected chromosomal region is present in an abnormal number of copies within a patient’s nuclei. The laboratory has a fluorescent DNA probe complementary to that region. What is the main diagnostic advantage of the appropriate technique?

Options:

Correct Answer: It demonstrates selected DNA sequences within cells

Explanation: FISH allows a fluorescent probe to hybridize with a specific chromosomal DNA sequence, permitting assessment of its presence, location or abnormal copy number in cells.

Question:

DNA extracted from a patient is cut into fragments and separated by electrophoresis. The fragments are then transferred to a membrane before addition of a labeled complementary probe. What is the purpose of the probe in this procedure?

Options:

Correct Answer: To detect a specific DNA sequence

Explanation: In Southern blotting, the labeled probe hybridizes with its complementary DNA sequence, identifying the particular fragment containing the sequence of interest.

Question:

A researcher suspects that a pathogenic mutation markedly reduces production of a particular protein. The aim is to determine whether that specific protein is present in the patient’s cells. Which laboratory component provides specificity in the most appropriate blotting technique?

Options:

Correct Answer: Specific antibody

Explanation: Western blotting identifies a selected protein using an antibody directed against that protein, allowing assessment of its presence and relative characteristics.

Question:

A laboratory is investigating two abnormalities in the same inherited disorder. The first requires analysis of a selected DNA sequence, while the second requires direct assessment of the resulting protein product. Which pairing best matches the molecular target?

Options:

Correct Answer: PCR for DNA; Western blot for protein

Explanation: PCR is directed at DNA sequences, whereas Western blotting examines proteins using specific antibodies. Selecting a test requires matching the method to the molecular target.

Question:

A genetic laboratory receives four requests: amplification of a selected gene region, localization of a chromosomal DNA sequence, detection of a particular DNA fragment, and detection of a specific protein. Which sequence of techniques correctly addresses these requests in the same order?

Options:

Correct Answer: PCR → FISH → Southern blot → Western blot

Explanation: PCR amplifies selected DNA, FISH localizes specific chromosomal sequences, Southern blot identifies selected DNA fragments, and Western blot detects specific proteins.