Molecular Genetics — MCQs

An 8-month-old infant is brought to the physician by his mother because of a 1-month history of progressive listlessness. His mother says, "He used to crawl around, but now he can't even keep himself upright. He seems so weak!" Pregnancy and delivery were uncomplicated. Examination shows hypotonia and an increased startle response. Genetic analysis show insertion of four bases (TATC) into exon 11. Further evaluation shows decreased activity of hexosaminidase A. Which of the following mutations best explains these findings?

A 26-year-old woman presents to a physician for genetic counseling, because she is worried about trying to have a child. Specifically, she had 2 siblings that died young from a lysosomal storage disorder and is afraid that her own children will have the same disorder. Her background is Ashkenazi Jewish, but she says that her husband's background is mixed European heritage. Her physician says that since her partner is not of Jewish background, their chance of having a child with Niemann-Pick disease is dramatically decreased. Which of the following genetic principles best explains why there is an increased prevalence of this disease in some populations?

A 5-year-old patient presents to the pediatrician's office with fatigue and swollen lymph nodes. Extensive work-up reveals a diagnosis of acute lymphoblastic leukemia. In an effort to better tailor the patient's treatments, thousands of genes are arranged on a chip and a probe is made from the patient's mRNA (converted to cDNA). This probe is then hybridized to the chip in order to measure the gene expression of thousands of genes. The technology used to investigate this patient's gene expression profile is best for detecting which of the following types of genetic abnormalities?

An investigator is studying the biology of human sperm cells. She isolates spermatogonia obtained on a testicular biopsy from a group of healthy male volunteers. She finds that the DNA of spermatogonia obtained from these men show a large number of TTAGGG sequence repeats. This finding can best be explained by increased activity of an enzyme with which of the following functions?

A 49-year-old man presents to your clinic with “low back pain”. When asked to point to the area that bothers him the most, he motions to both his left and right flank. He describes the pain as deep, dull, and aching for the past few months. His pain does not change significantly with movement or lifting heavy objects. He noted dark colored urine this morning. He has a history of hypertension managed with hydrochlorothiazide; however, he avoids seeing the doctor whenever possible. He drinks 3-4 beers on the weekends but does not smoke. His father died of a sudden onset brain bleed, and his mother has diabetes. In clinic, his temperature is 99°F (37.2°C), blood pressure is 150/110 mmHg, pulse is 95/min, and respirations are 12/min. Bilateral irregular masses are noted on deep palpation of the abdomen. The patient has full range of motion in his back and has no tenderness of the spine or paraspinal muscles. Urine dipstick in clinic is notable for 3+ blood. Which chromosome is most likely affected by a mutation in this patient?

A 3-year-old boy is brought to his pediatrician by his parents for a follow-up visit. Several concerning traits were observed at his last physical, 6 months ago. He had developmental delay, a delay in meeting gross and fine motor control benchmarks, and repetitive behaviors. At birth, he was noted to have flat feet, poor muscle tone, an elongated face with large, prominent ears, and enlarged testicles. He takes a chewable multivitamin every morning. There is one other member of the family, on the mother’s side, with a similar condition. Today, his blood pressure is 110/65 mm Hg, heart rate is 90/min, respiratory rate is 22/min, and temperature of 37.0°C (98.6°F). On physical exam, the boy repetitively rocks back and forth and has difficulty following commands. His heart has a mid-systolic click, followed by a late systolic murmur and his lungs are clear to auscultation bilaterally. Several vials of whole blood are collected for analysis. Which of the following studies should be conducted as part of the diagnostic screening protocol?

A 13-year-old girl is referred to an oral surgeon after complaining of tooth pain, especially in the upper jaw. A review of her medical history reveals status post-surgical repair of a patent ductus arteriosus when she was 6 years old. At the clinic, her temperature is 37.0ºC (98.6°F), pulse is 90/min, respirations are 18/min, and blood pressure is 110/78 mm Hg. On physical examination, her height is 157.5 cm (5 ft 2 in), her weight is 50 kg (110 lb) and her arms seem disproportionately long for her trunk. She also has arachnodactyly and moderate joint laxity. Intraoral examination reveals crowded teeth and a high arched palate. Which of the following protein is most likely defective in this condition?

An investigator is processing a blood sample from a human subject. A reagent is added to the sample and the solution is heated to break the hydrogen bonds between complementary base pairs. This solution is then cooled to allow artificial DNA primers in the solution to attach to the separated strands of the sample DNA molecules. An enzyme derived from the thermophilic bacterium Thermus aquaticus is added and the solution is reheated. These steps are repeated multiple times until the aim of the test is achieved. The investigator most likely used which of the following laboratory procedures on the test sample?

A group of scientists developed a mouse model to study nondisjunction in meiosis. Their mouse model produced gametes in the following ratio: 2 gametes with 24 chromosomes each and 2 gametes with 22 chromosomes each. In which of the following steps of meiosis did the nondisjunction occur?

A 10-year-old boy is brought to the physician because of recurring episodes of achy muscle pain in his legs. He has a history of poor school performance despite tutoring and has been held back two grades. He is at the 40th percentile for height and 30th percentile for weight. Examination shows ptosis, a high-arched palate, and muscle weakness in the face and hands; muscle strength of the quadriceps and hamstrings is normal. Sensation is intact. Percussion of the thenar eminence causes the thumb to abduct and then relax slowly. Which of the following is the most likely underlying cause?