Genetic Counseling — MCQs
All of the following are true about Down syndrome except for one.
Pedigree analysis chart is a tool used for which of the following purposes?
Which pattern of inheritance of disease is associated with consanguinity?
A GSP4 woman comes for routine sonography for the first time. She has four daughters and expresses a desire for a boy this time, asking for sex determination. To abide by ethical guidelines, what should you do?
Examine this pedigree chart carefully. What type of transmission does it depict?
The risk of recurrence of congenital heart disease for subsequent pregnancies in families with one affected child is:
What is the chance of a child having cystic fibrosis if both parents are carriers of the disease?
An investigator studying viral mutation isolates a virus strain from the gastric contents of an infant with gastroenteritis. This virus has a nonenveloped RNA genome with 11 segments and an icosahedral symmetrical capsid. The investigator finds that if 2 strains of this virus coinfect a single host cell, some of the resulting viral progeny have genome segments derived from both parental viruses. The observed phenomenon is most likely also seen in which of the following viral families?
A 12-year-old girl with a recently diagnosed seizure disorder is brought to the physician by her mother for genetic counseling. She has difficulties in school due to a learning disability. Medications include carbamazepine. She is at the 95th percentile for height. Genetic analysis shows a 47, XXX karyotype. An error in which of the following stages of cell division is most likely responsible for this genetic abnormality?
A homeless 45-year-old man presents to the emergency room in December complaining of malaise, body aches, chills, and fever. He reports that his symptoms started 4 days ago. His myalgias and chills have begun to resolve, but now he is starting to develop a dry cough, dyspnea, and a sore throat. He does not have a primary care provider and has not had any vaccinations in over 2 decades. He receives medical care from the emergency room whenever he is feeling ill. His temperature is 103°F (39.4°C), blood pressure is 130/70 mmHg, pulse is 115/min, and respirations are 22/min. On exam, he appears fatigued with mildly increased work of breathing. A chest radiograph is negative. A nasopharyngeal viral culture is positive for an orthomyxovirus. Upon further review of the patient’s medical record, he was diagnosed with the same condition 1 year ago in November. Which of the following mechanisms is responsible for pandemics of this patient’s disease?
Genetic Counseling US Medical PG Practice Questions and MCQs
Question 1: All of the following are true about Down syndrome except for one.
- A. Incidence of Robertsonian translocation is 1:1000 (Correct Answer)
- B. Most common cause is trisomy 21
- C. Mosaicism 21 has no association with maternal age
- D. Extra chromosome is of maternal origin
- E. Incidence increases with advanced maternal age
Explanation: **Incidence of Robertsonian translocation is 1:1000** - This statement is **not accurate** for Down syndrome. Robertsonian translocation accounts for only about **3-4% of Down syndrome cases**, not a general population incidence of 1:1000. - The vast majority of Down syndrome cases (~95%) are due to trisomy 21 from nondisjunction, not translocation. - This is the **correct answer** as it is the FALSE statement. *Extra chromosome is of maternal origin* - In approximately **90-95% of Down syndrome cases**, the extra copy of chromosome 21 originates from the mother due to **nondisjunction** during meiosis. - This maternal origin is strongly correlated with **advanced maternal age**. *Most common cause is trisomy 21* - **Trisomy 21** (due to meiotic nondisjunction) accounts for about **95% of all Down syndrome cases**, making it the most common genetic mechanism. - This results in three separate copies of chromosome 21 in all body cells. *Mosaicism 21 has no association with maternal age* - **Mosaic Down syndrome** occurs when nondisjunction happens *after fertilization* in early embryonic development, leading to a mixture of cells with normal and trisomic cells. - Because it is a **post-zygotic event**, its incidence is independent of **maternal age**, unlike full trisomy 21. *Incidence increases with advanced maternal age* - **TRUE statement** - The risk of Down syndrome (particularly trisomy 21) increases significantly with **maternal age**. - Risk is approximately 1:1500 at age 20, 1:1000 at age 30, 1:400 at age 35, and 1:100 at age 40. - This is due to increased risk of meiotic nondisjunction in older oocytes.
Question 2: Pedigree analysis chart is a tool used for which of the following purposes?
- A. Used for growth monitoring
- B. To assess side effects during chemotherapy
- C. To assess developmental delay in infants
- D. Used to see genetic transmission (Correct Answer)
Explanation: ***Used to see genetic transmission*** - A **pedigree chart** is a visual representation of biological relationships and genetic traits across multiple generations of a family. - It helps determine the **inheritance pattern** of a particular trait or disease within a family, such as autosomal dominant, recessive, or X-linked. *Used for growth monitoring* - **Growth monitoring** typically involves plotting an individual's weight, height, and head circumference on growth charts over time. - While family data might be considered, a pedigree chart is not the primary tool for directly monitoring an individual's physical growth. *To assess side effects during chemotherapy* - Assessing **side effects during chemotherapy** involves clinical evaluations, laboratory tests (e.g., blood counts, organ function tests), and patient self-reporting. - A pedigree chart provides information about family history and genetic predisposition, not direct monitoring of treatment side effects. *To assess developmental delay in infants* - **Developmental delay assessment** involves observing a child's milestone achievement in areas like motor skills, language, and cognition, often using standardized screening tools. - While some developmental delays can have genetic causes that might be highlighted in a pedigree, the chart itself does not directly assess developmental progress.
Question 3: Which pattern of inheritance of disease is associated with consanguinity?
- A. Autosomal dominant
- B. X linked recessive
- C. Autosomal recessive (Correct Answer)
- D. X linked dominant
Explanation: ***Autosomal recessive*** - Consanguineous relationships increase the likelihood of offspring inheriting **two copies of a rare deleterious recessive allele**, one from each parent [1]. - This occurs because relatives share a greater proportion of their genes, making it more probable that both parents are **heterozygous carriers** for the same recessive disorder. *Autosomal dominant* - In autosomal dominant disorders, only **one copy of the altered gene** is needed to cause the disease, so expression is not typically influenced by consanguinity. - These conditions often manifest in every generation and are not more prevalent with increased shared genetic material. *X-linked recessive* - X-linked recessive disorders primarily affect males, as they only have one X chromosome, and are transmitted by carrier females. - While consanguinity can theoretically increase the carrier rate within a population, its direct impact on the inheritance pattern of an X-linked trait in a single family is less pronounced compared to autosomal recessive conditions. *X-linked dominant* - X-linked dominant disorders are expressed in heterozygous females and hemizygous males, with affected males often having more severe disease. - The inheritance pattern is not significantly influenced by consanguinity, as only one copy of the affected gene on the X chromosome is sufficient for disease manifestation.
Question 4: A GSP4 woman comes for routine sonography for the first time. She has four daughters and expresses a desire for a boy this time, asking for sex determination. To abide by ethical guidelines, what should you do?
- A. Check routine ANC and sex for developmental abnormalities and do not reveal gender to the patient (Correct Answer)
- B. Check routine ANC and sex for developmental abnormalities and do reveal gender to the patient
- C. Do reveal gender if a girl
- D. Check only routine ANC, do not check sex
Explanation: ***Check routine ANC and sex for developmental abnormalities and do not reveal gender to the patient*** - It is **illegal** and **unethical** to reveal the sex of the fetus in many countries, including India, to prevent **sex-selective abortions**. - The primary purpose of a routine antenatal ultrasound is to assess fetal **health** and **developmental abnormalities**, not to determine sex for parental preference. *Check routine ANC and sex for developmental abnormalities and do reveal gender to the patient* - Revealing the gender to the patient directly facilitates **sex-selective abortion**, which is medically unethical and illegal due to the potential for harm to the fetus and society. - This practice would violate the **Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act** in India, which prohibits gender determination. *Do reveal gender if a girl* - Revealing the gender, regardless of whether it is a boy or a girl, can lead to **gender-biased selective abortions**, particularly in cultures with a strong preference for male offspring. - This action undermines the ethical principles of **non-maleficence** and **justice** by potentially facilitating harm based on gender preference. *Check only routine ANC, do not check sex* - While the primary focus is routine antenatal care, avoiding the assessment of fetal sex entirely could lead to **missing potential developmental abnormalities** that might be identifiable through observation of external genitalia. - A thorough ultrasound examination routinely includes a visual check of fetal anatomy, which can incidentally reveal gender, but this information should not be shared with the parents for selection purposes.
Question 5: Examine this pedigree chart carefully. What type of transmission does it depict?
- A. AR Inheritance
- B. AD Inheritance
- C. Holandric Inheritance (Correct Answer)
- D. X-Linked Recessive
Explanation: ***Holandric Inheritance*** - **Holandric inheritance** (Y-linked) shows the trait appearing only in **males** and being transmitted from **father to all his sons**. - The pedigree demonstrates classic **father-to-son transmission** pattern where affected fathers (I-1 and II-3) pass the trait to all their male offspring. *AR Inheritance* - **Autosomal recessive** traits typically **skip generations** and affect both males and females equally. - Affected individuals usually have **unaffected carrier parents**, which is not consistently observed in this pedigree. *AD Inheritance* - **Autosomal dominant** traits affect both sexes equally and show **vertical transmission** through generations. - An affected father would pass the trait to approximately **50% of all children** regardless of sex, not exclusively to sons. *X-Linked Recessive* - **X-linked recessive** inheritance affects males predominantly, but **affected fathers cannot pass** the trait to their sons. - Sons receive the **Y chromosome from father** and X chromosome from mother, making father-to-son transmission impossible.
Question 6: The risk of recurrence of congenital heart disease for subsequent pregnancies in families with one affected child is:
- A. 10-12%
- B. 1%
- C. 2-6% (Correct Answer)
- D. 0.80%
Explanation: ***2-6%*** - The recurrence risk for **congenital heart disease (CHD)** in subsequent pregnancies after one affected child is generally cited as **2-6%**, reflecting an increased familial predisposition. - This risk is higher than the general population risk but still relatively low, primarily due to the complex, multifactorial etiology of most CHDs. *10-12%* - A **10-12% recurrence risk** is generally too high for most common congenital heart defects, which are typically multifactorial. - Such a high risk might be seen in specific **syndromic forms** of CHD (e.g., genetic aneuploidies or single gene defects), but not for isolated CHD in general. *1%* - A **1% recurrence risk** is comparable to the general population incidence of congenital heart disease (approximately 0.8-1%). - This value does not adequately reflect the established **increased risk for siblings** of an affected child, which is known to be higher than the background population risk. *0.80%* - **0.80%** represents the approximate **general population incidence** of congenital heart disease in live births without a prior affected sibling. - This figure does not account for the **increased familial risk** that exists once one child in a family is already affected.
Question 7: What is the chance of a child having cystic fibrosis if both parents are carriers of the disease?
- A. 75%
- B. 25% (Correct Answer)
- C. 50%
- D. 0%
- E. 100%
Explanation: ***50%*** - If one parent is affected by cystic fibrosis (CF), they are **homozygous for the CFTR mutation**, while the normal parent is likely **homozygous for the normal allele**. - Each child has a **50% chance** of inheriting the **mutated allele** from the affected parent, resulting in an **autosomal recessive** inheritance pattern [1]. *70%* - This percentage does not reflect the inheritance probabilities associated with **autosomal recessive traits** [1], such as cystic fibrosis. - In heterozygous and normal arrangements, the calculation does not support a **70%** inheritance chance of the disease. *80%* - Similarly, an **80% chance** is inaccurate as cystic fibrosis requires two mutated alleles for the disease to manifest [1]. - The inheritance pattern does not allow for a higher than **50% chance** when one parent is normal. *25%* - A **25% chance** applies if both parents were carriers of the CFTR mutation [1]. However, with only one affected parent, this percentage does not apply. - The maximum **chance of inheritance** from one affected and one normal parent is accurately stated as **50%**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 53-54.
Question 8: An investigator studying viral mutation isolates a virus strain from the gastric contents of an infant with gastroenteritis. This virus has a nonenveloped RNA genome with 11 segments and an icosahedral symmetrical capsid. The investigator finds that if 2 strains of this virus coinfect a single host cell, some of the resulting viral progeny have genome segments derived from both parental viruses. The observed phenomenon is most likely also seen in which of the following viral families?
- A. Caliciviruses
- B. Orthomyxoviruses (Correct Answer)
- C. Flaviviruses
- D. Retroviruses
- E. Picornaviruses
Explanation: ***Orthomyxoviruses*** - The description of a virus with a **segmented RNA genome** undergoing reassortment (mixing segments from coinfecting strains) is characteristic of **Orthomyxoviruses**, which notably include the influenza virus. - Influenza virus is well-known for its ability to **reassort** its **8 segmented RNA genome**, leading to antigenic shifts responsible for pandemics. *Caliciviruses* - **Caliciviruses** (e.g., Norovirus) have a **single-stranded, non-segmented RNA genome** and do not undergo genomic reassortment. - They are a common cause of **gastroenteritis** but their genetic features differ. *Flaviviruses* - **Flaviviruses** (e.g., Dengue, Yellow Fever, Zika) possess a **single-stranded, non-segmented RNA genome**. - They replicate via a polyprotein cleavage mechanism and do not exhibit genomic reassortment. *Retroviruses* - **Retroviruses** (e.g., HIV) have a **diploid, positive-sense, single-stranded RNA genome** that is reverse transcribed into DNA. - While they can undergo **recombination** during reverse transcription, this is distinct from the described reassortment of segmented genomes. *Picornaviruses* - **Picornaviruses** (e.g., Poliovirus, Rhinovirus) have a **single-stranded, non-segmented RNA genome**. - They are known for their rapid replication but do not exhibit genomic segmentation or reassortment.
Question 9: A 12-year-old girl with a recently diagnosed seizure disorder is brought to the physician by her mother for genetic counseling. She has difficulties in school due to a learning disability. Medications include carbamazepine. She is at the 95th percentile for height. Genetic analysis shows a 47, XXX karyotype. An error in which of the following stages of cell division is most likely responsible for this genetic abnormality?
- A. Paternal meiosis, anaphase I
- B. Maternal meiosis, telophase II
- C. Maternal meiosis, metaphase II
- D. Paternal meiosis, metaphase II
- E. Maternal meiosis, anaphase II (Correct Answer)
Explanation: ***Maternal meiosis, anaphase II*** - A 47,XXX karyotype indicates an extra X chromosome, which most commonly results from **nondisjunction during maternal meiosis**. - **Nondisjunction in anaphase II** occurs when sister chromatids fail to separate properly, leading to an ovum containing two X chromosomes, which upon fertilization by an X-bearing sperm results in an XXX zygote. - While nondisjunction can occur in either meiosis I or II, both produce the same 47,XXX outcome; anaphase is the critical stage where chromosome separation occurs. *Paternal meiosis, anaphase I* - Nondisjunction during paternal meiosis I would lead to sperm with either no sex chromosomes or both X and Y chromosomes, resulting in **45,X0 (Turner syndrome) or 47,XXY (Klinefelter syndrome)** upon fertilization, not 47,XXX. - This involves improper segregation of **homologous chromosomes**. *Maternal meiosis, telophase II* - While telophase II is the final stage of meiosis II, the critical event of nondisjunction (failure of sister chromatids to separate) occurs during **anaphase II**, not telophase. - Errors in telophase II would affect nuclear reformation but do not cause the chromosomal separation failure responsible for **aneuploidy**. *Maternal meiosis, metaphase II* - Metaphase II is when sister chromatids align at the metaphase plate; while improper alignment could theoretically contribute to aneuploidy, the actual **physical separation failure** defining nondisjunction occurs during **anaphase II**. - Nondisjunction is specifically an anaphase phenomenon. *Paternal meiosis, metaphase II* - Paternal meiosis II nondisjunction would result in sperm carrying either two sex chromosomes (XX or YY) or none, leading to karyotypes like **47,XYY or 47,XXY**, not 47,XXX. - Paternal contribution of two X chromosomes would require the rare scenario of an X-bearing sperm with nondisjunction fertilizing an X-bearing ovum that also had nondisjunction, which is extremely unlikely.
Question 10: A homeless 45-year-old man presents to the emergency room in December complaining of malaise, body aches, chills, and fever. He reports that his symptoms started 4 days ago. His myalgias and chills have begun to resolve, but now he is starting to develop a dry cough, dyspnea, and a sore throat. He does not have a primary care provider and has not had any vaccinations in over 2 decades. He receives medical care from the emergency room whenever he is feeling ill. His temperature is 103°F (39.4°C), blood pressure is 130/70 mmHg, pulse is 115/min, and respirations are 22/min. On exam, he appears fatigued with mildly increased work of breathing. A chest radiograph is negative. A nasopharyngeal viral culture is positive for an orthomyxovirus. Upon further review of the patient’s medical record, he was diagnosed with the same condition 1 year ago in November. Which of the following mechanisms is responsible for pandemics of this patient’s disease?
- A. Reassortment (Correct Answer)
- B. Complementation
- C. Transduction
- D. Phenotypic mixing
- E. Recombination
Explanation: ***Reassortment*** - This patient presents with **influenza**, confirmed by a positive nasopharyngeal viral culture for an **orthomyxovirus**. The seasonal nature of his illness, despite having it before, points to antigenic changes. - **Reassortment** (also known as **antigenic shift**) is the primary mechanism responsible for **influenza pandemics**. It involves the exchange of entire gene segments between different influenza strains (e.g., human and avian or swine strains) when a host cell is co-infected with two distinct viral strains, leading to a new subtype with novel hemagglutinin (HA) or neuraminidase (NA) proteins that human populations have little to no immunity against. *Complementation* - **Complementation** occurs when two viruses infect the same cell, and one virus provides a **necessary gene product** that the other mutated or defective virus lacks, allowing the latter to replicate. - This mechanism does not involve genetic exchange leading to new viral subtypes and is therefore not responsible for the emergence of pandemic strains. *Transduction* - **Transduction** is a process by which **bacteriophages** (viruses that infect bacteria) transfer bacterial DNA from one bacterium to another. - This is a mechanism of gene transfer in bacteria and is not relevant to the genetic changes in influenza viruses. *Phenotypic mixing* - **Phenotypic mixing** occurs when the genome of one virus is packaged into the **capsid** of another virus, or when genetic material from two viruses is packaged into a mixed capsid. - While it can alter the tropism or antigenicity of progeny viruses temporarily, it does not involve a change in the viral genome itself and is therefore not responsible for permanent shifts leading to pandemics. *Recombination* - **Recombination** involves the exchange of genetic material between two homologous DNA or RNA molecules, leading to new combinations of genes within the same gene segment. - While recombination can occur in viruses, **reassortment** of entire gene segments (antigenic shift) is the specific and most significant mechanism for creating novel influenza strains capable of causing pandemics, rather than recombination within gene segments.
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