49 Year 2: Molecular Genetics and Cytogenetics exam questions on COMPLEX MULTIGENIC AND CYTOGENETIC DISORDERS - 50 MCQs for medical students. Includes MCQs, ans
This MCQ set contains 49 questions on COMPLEX MULTIGENIC AND CYTOGENETIC DISORDERS - 50 MCQs in the Year 2: Molecular Genetics and Cytogenetics unit. Each question includes the correct answer and a detailed explanation for active recall and exam preparation.
Correct answer: B – 1%
A polymorphism is defined as a genetic variant that has at least two alleles and occurs in at least 1% of the population.
Correct answer: C – More than 50%
Of the 20 to 30 genes implicated in type 1 diabetes, a few HLA alleles contribute more than 50% of the risk, demonstrating that different polymorphisms vary significantly in their contribution.
Correct answer: B – Obesity
Type 2 diabetes often first manifests clinically after weight gain, demonstrating how obesity as an environmental factor unmasks the diabetic genetic trait.
Correct answer: C – 1 in 200
It is estimated that approximately 1 in 200 newborn infants has some form of chromosomal abnormality.
Correct answer: C – 50%
Approximately 50% of first-trimester spontaneous abortions are associated with chromosomal abnormalities.
Correct answer: B – Giemsa stain (G banding)
The Giemsa stain (G banding) technique is widely used and produces a distinctive pattern of alternating light and dark bands that allows identification of each chromosome.
Correct answer: B – Polyploid
Any exact multiple of the haploid number (n) is called euploid, and numbers such as 3n and 4n are specifically called polyploid.
Correct answer: C – Nondisjunction during meiosis
The chief cause of aneuploidy is nondisjunction of a homologous pair of chromosomes at the first meiotic division or failure of sister chromatids to separate during the second meiotic division.
Correct answer: C – 2n + 1
When a gamete with an extra chromosome (n + 1) is fertilized by a normal gamete (n), the resulting zygote is trisomic with chromosome count of 2n + 1.
Correct answer: C – Sex chromosome imbalances
Imbalances of sex chromosomes (excess or loss) are tolerated much better than similar imbalances of autosomes, often producing subtle abnormalities. --- SECTION B: CHROMOSOMAL TERMINOLOGY & NOTATION (Questions 11-16)
Correct answer: B – Presence of two or more cell populations with different chromosome complements
Mosaicism is the presence of two or more populations of cells with different complements of chromosomes in the same individual, commonly affecting sex chromosomes.
Correct answer: C – Short arm (petit)
In cytogenetic shorthand, "p" (French, petit) denotes the short arm of a chromosome, while "q" denotes the long arm.
Correct answer: B – Reciprocal translocation between chromosomes 2 and 5
This notation indicates a reciprocal translocation involving the long arm of chromosome 2 at region 3, band 1, and the short arm of chromosome 5, region 1, band 4.
Correct answer: B – Translocation between two acrocentric chromosomes
Robertsonian (centric fusion) translocation is a reciprocal translocation between two acrocentric chromosomes involving the short arm of one and long arm of the other.
Correct answer: B – i(Xq)
The most common isochromosome present in live births involves the long arm of the X chromosome and is designated i(Xq), resulting in monosomy for Xp genes and trisomy for Xq genes.
Correct answer: B – Horizontal division of centromere
Isochromosomes result when the centromere divides horizontally rather than vertically, leading to loss of one arm and duplication of the remaining arm. --- SECTION C: DOWN SYNDROME (TRISOMY 21) (Questions 17-27)
Correct answer: C – 95%
About 95% of affected persons with Down syndrome have trisomy 21, with a chromosome count of 47, most commonly caused by meiotic nondisjunction.
Correct answer: C – 1 in 25
Down syndrome occurs in 1 in 1550 live births in women younger than 20 years but increases dramatically to 1 in 25 live births in women older than 45 years.
Correct answer: D – 95%
In 95% of Down syndrome cases, the extra chromosome is of maternal origin, supporting that meiotic nondisjunction occurs primarily in the ovum.
Correct answer: B – 4%
In about 4% of all patients with trisomy 21, the extra chromosomal material is present as a translocation of the long arm of chromosome 21 to chromosome 22 or 14.
Correct answer: A – 1%
Approximately 1% of patients with trisomy 21 are mosaics, usually having a mixture of 46- and 47-chromosome cells resulting from mitotic nondisjunction during embryogenesis.
Correct answer: C – 40%
Approximately 40% of Down syndrome patients have congenital heart disease, most commonly endocardial cushion defects including atrial septal defects and ventricular septal defects.
Correct answer: C – 10- to 20-fold
Children with trisomy 21 have a 10- to 20-fold increased risk of developing acute leukemia, including both acute lymphoblastic leukemias and acute myeloid leukemias.
Correct answer: B – Over age 40
Virtually all patients with trisomy 21 older than age 40 develop neuropathologic changes characteristic of Alzheimer disease.
Correct answer: C – 47 years
Improved medical care has increased the longevity of persons with trisomy 21, with the current median age at death being 47 years, up from 25 years in 1983.