60 Year 2: Molecular Genetics and Cytogenetics exam questions on Genetic Disorders MCQ Examination (Part 2) for medical students. Includes MCQs, answers, explan
This MCQ set contains 60 questions on Genetic Disorders MCQ Examination (Part 2) 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 – Polymorphism
A polymorphism is defined as a genetic variant that has at least two alleles and occurs in at least 1% of the population, distinguishing it from rare mutations.
Correct answer: B – 6-7 genes
While 20-30 genes are implicated in type 1 diabetes, only 6-7 are most important, with a few HLA alleles contributing more than 50% of the risk.
Correct answer: B – Obesity and weight gain
Type 2 diabetes has features of a complex multigenic disorder where obesity and weight gain often unmask the diabetic genetic trait, demonstrating gene-environment interaction.
Correct answer: C – 50%
Approximately 50% of first-trimester spontaneous abortions have demonstrable chromosomal abnormalities, highlighting the importance of chromosomal integrity for fetal development.
Correct answer: C – Giemsa stain
The G-banding (Giemsa banding) technique is widely used to stain chromosomes, producing distinctive patterns of alternating light and dark bands that allow identification of each chromosome.
Correct answer: A – Euploid and polyploid
69 chromosomes (3n) is an exact multiple of the haploid number (n=23), making it euploid. Since it's a multiple other than 2n, it's also polyploid (specifically triploid).
Correct answer: C – Nondisjunction during meiosis
Nondisjunction of homologous chromosomes during the first meiotic division or failure of sister chromatids to separate during the second meiotic division is the chief cause of aneuploidy.
Correct answer: B – Incompatible with life
Monosomy involving an autosome is incompatible with life, whereas trisomies of certain autosomes and monosomy of sex chromosomes can be compatible with life.
Correct answer: B – Presence of two or more populations of cells with different chromosome complements
Mosaicism is the presence of two or more populations of cells with different complements of chromosomes in the same individual, usually resulting from postzygotic mitotic nondisjunction.
Correct answer: B – The short arm of a chromosome
In cytogenetic shorthand, "p" (from French "petit") denotes the short arm of a chromosome, while "q" denotes the long arm.
Correct answer: C – 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 at region 1 band 4.
Correct answer: B – Two acrocentric chromosomes
Robertsonian (centric) fusion is a reciprocal translocation between two acrocentric chromosomes, involving the short arm of one and long arm of the other, forming one large and one very small chromosome.
Correct answer: B – Long arm of the X chromosome [i(Xq)]
The most common isochromosome in live births is i(Xq), involving the long arm of the X chromosome, resulting in monosomy for Xp genes and trisomy for Xq genes.
Correct answer: B – Horizontal division of the centromere
Isochromosomes result when the centromere divides horizontally (rather than vertically), leading to loss of one arm and duplication of the other, creating two identical arms.
Correct answer: C – Loss of chromosomal material produces more severe defects than gain
In general, loss of chromosomal material produces more severe defects than does gain of chromosomal material, which is why monosomies are typically more severe than trisomies.
Correct answer: B – Tolerated much better
Imbalances of sex chromosomes (excess or loss) are tolerated much better than similar imbalances of autosomes, often producing subtle abnormalities.
Correct answer: C – Down syndrome
QTLs are normal phenotypic characteristics governed by multigenic inheritance showing continuous variation, including hair color, eye color, height, and intelligence. Down syndrome is a chromosomal disorder.
Correct answer: C – Trisomy 21 (Down syndrom
Trisomy 21 (Down syndrome) is the most common chromosomal disorder, occurring with notable frequency compared to other chromosomal abnormalities.
Correct answer: B – Maternal origin
In approximately 95% of trisomy 21 cases, the extra chromosome is of maternal origin, resulting from meiotic nondisjunction in the ovum.
Correct answer: C – Meiotic nondisjunction form
Maternal age has a strong influence on Down syndrome due to meiotic nondisjunction (95% of cases), with incidence increasing dramatically with advancing maternal age.
Correct answer: B – 4%
About 4% of trisomy 21 patients have the extra chromosomal material as a translocation of the long arm of chromosome 21 to chromosome 22 or 14, often familial.
Correct answer: A – 1%
Approximately 1% of trisomy 21 patients are mosaics with a mixture of 46- and 47-chromosome cells, resulting from mitotic nondisjunction during early embryogenesis.
Correct answer: C – Endocardial cushion defects
Approximately 40% of Down syndrome patients have congenital heart disease, most commonly endocardial cushion defects including atrial 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 and acute myeloid leukemias.
Correct answer: B – Alzheimer disease
Virtually all patients with trisomy 21 older than age 40 develop neuropathologic changes characteristic of Alzheimer disease.