Q: Which of the following equations correctly calculates the sensitivity of a genetic screening test?

$$\text{Sensitivity} = \frac{\text{TP}}{\text{TP} + \text{FN}}$$

Q: A population screening test for PKU yields 450 true positives (TP), 35 false positives (FP), 55 false negatives (FN), and 825 true negatives (TN). What is the positive predictive value (PPV) of the test?

$$\text{PPV} = \frac{450}{450 + 35} = 0.928$$

Q: A researcher is studying the heritability of hypertension using twin studies. Monozygotic (MZ) twins have a concordance rate of 0.60, while dizygotic (DZ) twins have a concordance rate of 0.30. What is the estimated heritability ($$h^2) of $$hypertension in this population?

$$h^2 = 2$$ \times (0.60 - 0.30) = 0.60$$

Question 1

A 6-year-old child is diagnosed with bilateral retinoblastoma. Genetic testing reveals a germline mutation in the RB1 gene. According to Knudson's two-hit hypothesis, which of the following best explains the development of this cancer in the child?

Accepted Answer

Both alleles of the RB1 gene must be mutated, with one inherited and one acquired somatically.

Question 2

Which of the following best describes the function of the p53 protein in the regulation of the cell cycle?

Accepted Answer

It acts as a transcription factor that can induce cell cycle arrest or apoptosis in response to DNA damage.

Question 3

A woman with a family history of breast and ovarian cancer tests positive for a BRCA1 mutation. Which of the following statements about her cancer risk is most accurate?

Accepted Answer

She has a significantly increased lifetime risk for both breast and ovarian cancer compared to the general population.

Question 4

Which of the following equations correctly calculates the sensitivity of a genetic screening test?

Accepted Answer

$$	ext{Sensitivity} = \frac{	ext{TP}}{	ext{TP} + 	ext{FN}}$$

Question 5

A population screening test for PKU yields 450 true positives (TP), 35 false positives (FP), 55 false negatives (FN), and 825 true negatives (TN). What is the positive predictive value (PPV) of the test?

Accepted Answer

$$	ext{PPV} = \frac{450}{450 + 35} = 0.928$$

Question 6

Which of the following is a key difference between oncogenes and tumor suppressor genes in cancer development?

Accepted Answer

Oncogenes are typically dominant, requiring only one mutated allele to promote cancer, while tumor suppressor genes are recessive, requiring both alleles to be inactivated.

Question 7

A patient is diagnosed with Familial Adenomatous Polyposis (FAP). Which gene is most commonly mutated in this condition, and what is the associated lifetime risk of colon cancer if untreated?

Accepted Answer

APC gene; nearly 100% lifetime risk of colon cancer if untreated.

Question 8

In the context of multifactorial inheritance, which of the following best describes the liability threshold model?

Accepted Answer

A disease manifests only when an individual's combined genetic and environmental liability exceeds a certain threshold.

Question 9

A researcher is studying the heritability of hypertension using twin studies. Monozygotic (MZ) twins have a concordance rate of 0.60, while dizygotic (DZ) twins have a concordance rate of 0.30. What is the estimated heritability ($$h^2) of $$hypertension in this population?

Accepted Answer

$$h^2 = 2$$ 	imes (0.60 - 0.30) = 0.60$$

Question 10

Which of the following best explains why inborn errors of metabolism are good candidates for postnatal population screening?

Accepted Answer

Presymptomatic detection and early intervention can prevent or reverse disease progression.

Question 11

A 35-year-old man is found to have a mutation in the MLH1 gene. Which hereditary cancer syndrome is most likely associated with this mutation, and what is a key feature of this syndrome?

Accepted Answer

Lynch syndrome; increased risk of colorectal and endometrial cancers.

Question 12

Which of the following is NOT a general feature of multifactorial inheritance?

Accepted Answer

Traits show a clear Mendelian pattern of inheritance.

Question 13

A laboratory test for a genetic disorder yields the following results: 200 true positives (TP), 20 false positives (FP), 40 false negatives (FN), and 800 true negatives (TN). What is the prevalence of the disorder in the tested population?

Accepted Answer

$$	ext{Prevalence} = \frac{	ext{TP} + 	ext{FN}}{	ext{TP} + 	ext{FP} + 	ext{FN} + 	ext{TN}} = \frac{200 + 40}{200 + 20 + 40 + 800} = \frac{240}{1060} \approx 0.226$$

Question 14

Which of the following best describes the role of telomerase in cancer cell immortality?

Accepted Answer

Telomerase maintains telomere length, allowing cancer cells to divide indefinitely.

Question 15

A child is born with a rare metabolic disorder due to a defect in the LDL receptor gene (LDLR). Which inheritance pattern and disease is most likely?

Accepted Answer

Autosomal dominant; Familial Hypercholesterolemia

Question 16

Which of the following is a function of cyclin-dependent kinases (CDKs) in the cell cycle?

Accepted Answer

They phosphorylate target proteins to regulate progression through cell cycle checkpoints.

Question 17

A pedigree shows a trait that appears in both sexes, skips generations, and is more common among siblings than in the general population. Which mode of inheritance is most likely?

Accepted Answer

Autosomal recessive

Question 18

Which of the following best describes a 'driver mutation' in cancer?

Accepted Answer

A mutation that confers a growth advantage to the cell and contributes to cancer development.

Question 19

Which of the following is NOT a principle of population screening for genetic diseases?

Accepted Answer

The screening test can be difficult and time-consuming as long as it is valid and reliable.

Question 20

A 2-year-old child presents with a white pupillary reflex and is diagnosed with unilateral retinoblastoma. The father had unilateral retinoblastoma, and the uncle had bilateral retinoblastoma. What is the most likely explanation for the inheritance pattern in this family?

Accepted Answer

Autosomal dominant inheritance with incomplete penetrance of the RB1 gene mutation.

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