United States Medical Licensing Step 1: USMLE-STEP-1

Correct Answer: E

Section: Biochemistry DNAfingerprinting refers to the process of using polymorphic repeat sequences to establish a unique pattern of DNA fragments for any given individual. The polymorphic repeats that are identifiable by the fingerprinting technique are hypervariable repeats such as variable number tandem repeats (VNTRs). The bands are detected by Southern blotting enzyme-digested chromosomal DNA and probing the blot with various different VNTR probes. The generation of a DNA library (choice A) refers to the establishment of a complete collection of cloned fragments of DNA, either from genomic sources or cDNA. DNA footprinting (choice B) refers to the identification of sequences of DNA to which specific proteins bind, thereby rendering the DNA at that site resistant to digestion by DNA degrading nucleases. Hybridization (choice C) refers to the specific association of complimentary strands of DNA to one another. The PCR technique (choice D) uses synthetic oligonucleotides to direct the enzymatic amplification of specific sequences of DNA.

Correct Answer: A

Section: Behavioral Science and Biostatics Acommon cause of disruptiveness is attention deficit hyperactivity disorder (ADHD), which is characterized by inattention and hyperactivity. Enuresis (choice E), cruelty to animals (choice D), and trouble with the law (choice B) are often found in the childhoods of those who are eventually diagnosed as having an antisocial personality, but disruptiveness in class is more indicative of hyperactivity. Exploring Sean's relationship to his mother (choice C) may be useful, but not as much as assessing his attention span.

Correct Answer: B

Section: Behavioral Science and Biostatics The diagnostic criteria for ADHD include inattention, hyperactivity, and impulsivity invarious areas, and the symptoms must have been present before the age of 7. The specific history of inattention and hyperactivity tend to rule out choices A, C, D, and E, although there may be some elements of conduct disorder.