Genetic Disorders MCQ Examination (Part 2) | MCQ Quiz | OmpathStudy Kenya

Question 1

A genetic variant with at least two alleles occurring in at least 1% of the population is termed

Accepted Answer

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.

Question 2

In type 1 diabetes, approximately how many genes contribute most significantly to disease risk?

Accepted Answer

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.

Question 3

Which environmental factor commonly unmasks the genetic trait in type 2 diabetes mellitus?

Accepted Answer

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.

Question 4

Approximately what percentage of first-trimester spontaneous abortions have chromosomal abnormalities?

Accepted Answer

50% — Approximately 50% of first-trimester spontaneous abortions have demonstrable chromosomal abnormalities, highlighting the importance of chromosomal integrity for fetal development.

Question 5

The G-banding technique uses which stain to visualize chromosomes?

Accepted Answer

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.

Question 6

A chromosome number of 69 (3n) would be classified as

Accepted Answer

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).

Question 7

The chief cause of aneuploidy is

Accepted Answer

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.

Question 8

Monosomy involving an autosome is

Accepted Answer

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.

Question 9

Mosaicism is defined as

Accepted Answer

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.

Question 10

In cytogenetic notation, "p" denotes

Accepted Answer

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.

Question 11

The notation 46,XX,t(2;5)(q31;p14) indicates

Accepted Answer

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.

Question 12

Robertsonian translocation typically involves

Accepted Answer

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.

Question 13

The most common isochromosome in live births involves

Accepted Answer

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.

Question 14

An isochromosome results from

Accepted Answer

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.

Question 15

Which statement about chromosomal abnormalities is correct?

Accepted Answer

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.

Question 16

Sex chromosome imbalances compared to autosomal imbalances are

Accepted Answer

Tolerated much better — Imbalances of sex chromosomes (excess or loss) are tolerated much better than similar imbalances of autosomes, often producing subtle abnormalities.

Question 17

Quantitative trait loci (QTLs) include all of the following EXCEPT

Accepted Answer

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.

Question 18

The most common chromosomal disorder is

Accepted Answer

Trisomy 21 (Down syndrom — Trisomy 21 (Down syndrome) is the most common chromosomal disorder, occurring with notable frequency compared to other chromosomal abnormalities.

Question 19

In about 95% of Down syndrome cases, the extra chromosome 21 is of

Accepted Answer

Maternal origin — In approximately 95% of trisomy 21 cases, the extra chromosome is of maternal origin, resulting from meiotic nondisjunction in the ovum.

Question 20

Maternal age has the strongest correlation with which type of Down syndrome?

Accepted Answer

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.

Question 21

The translocation form of Down syndrome accounts for approximately what percentage of cases?

Accepted Answer

25% — 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.

Question 22

Mosaic Down syndrome accounts for approximately what percentage of cases?

Accepted Answer

10% — Approximately 1% of trisomy 21 patients are mosaics with a mixture of 46- and 47-chromosome cells, resulting from mitotic nondisjunction during early embryogenesis.

Question 23

Which cardiac defect is most common in Down syndrome?

Accepted Answer

Endocardial cushion defects — Approximately 40% of Down syndrome patients have congenital heart disease, most commonly endocardial cushion defects including atrial and ventricular septal defects.

Question 24

Children with trisomy 21 have what increased risk of developing acute leukemia?

Accepted Answer

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.

Question 25

Most Down syndrome patients older than 40 develop neuropathologic changes characteristic of

Accepted Answer

Alzheimer disease — Virtually all patients with trisomy 21 older than age 40 develop neuropathologic changes characteristic of Alzheimer disease.

Question 26

The current median age at death for persons with Down syndrome is

Accepted Answer

47 years — Improved medical care has increased longevity in Down syndrome from a median of 25 years in 1983 to currently 47 years.

Question 27

Most Down syndrome patients have an IQ in which range?

Accepted Answer

25 to 50 — Down syndrome is a leading cause of severe mental retardation; approximately 80% have an IQ of 25 to 50.

Question 28

Trisomy 18 is also known as

Accepted Answer

Edwards syndrome — Trisomy 18 is also known as Edwards syndrome, occurring less commonly than trisomy 21 and associated with severe malformations and early death.

Question 29

Trisomy 13 is also known as

Accepted Answer

Patau syndrome — Trisomy 13 is also known as Patau syndrome, associated with increased maternal age, severe malformations, and death usually within the first year of life.

Question 30

The 22q11.2 deletion syndrome was previously thought to represent which two separate disorders?

Accepted Answer

DiGeorge syndrome and velocardiofacial syndrome — The 22q11.2 deletion syndrome encompasses what were previously believed to be two different disorders: DiGeorge syndrome and velocardiofacial syndrome.

Question 31

Which gene on chromosome 22 is suspected to be responsible for DiGeorge syndrome features?

Accepted Answer

TBX1 — The transcription factor gene TBX1 in the 22q11.2 region is suspected to be responsible for DiGeorge syndrome features, as its loss correlates with syndrome occurrence.

Question 32

Patients with 22q11.2 deletion are at particularly high risk for

Accepted Answer

Psychoses such as schizophrenia and bipolar disorder — In addition to malformations, patients with 22q11.2 deletion are at particularly high risk for developing psychoses such as schizophrenia and bipolar disorder.

Question 33

The diagnosis of 22q11.2 deletion syndrome is established by

Accepted Answer

Fluorescence in situ hybridization (FISH) — While diagnosis may be suspected clinically, it can only be established by detection of the deletion using fluorescence in situ hybridization (FISH).

Question 34

Clinical features of 22q11.2 deletion syndrome include all EXCEPT

Accepted Answer

Hepatomegaly with cirrhosis — Features include cardiac defects, palate abnormalities, facial dysmorphism, developmental delay, thymic hypoplasia, and parathyroid hypoplasia. Hepatic involvement is not characteristic.

Question 35

When T cell immunodeficiency and hypocalcemia dominate in 22q11.2 deletion, the patient is said to have

Accepted Answer

DiGeorge syndrome — When T cell immunodeficiency and hypocalcemia are dominant features, patients are said to have DiGeorge syndrome, while velocardiofacial syndrome has pronounced dysmorphology and cardiac defects.

Question 36

According to the common disease-common variant hypothesis, complex disorders occur when

Accepted Answer

Many polymorphisms with modest effects are co-inherited — Complex multigenic disorders occur when many polymorphisms, each with modest effect and low penetrance, are co-inherited, according to the common disease-common variant hypothesis.

Question 37

A ring chromosome forms when

Accepted Answer

Segments are lost from each end and arms unite — A ring chromosome is a variant of deletion where, after loss of segments from each end of the chromosome, the remaining arms unite to form a ring structure.

Question 38

Deletion of which chromosome's short arm causes cri du chat syndrome?

Accepted Answer

Chromosome 5 — Cri du chat syndrome results from partial deletion of the short arm of chromosome 5 (5p-), named for the characteristic cat-like cry of affected infants.

Question 39

An inversion occurs when

Accepted Answer

Two interstitial breaks occur and segment reunites after turnaround — Inversions occur when there are two interstitial breaks in a chromosome and the segment between them reunites after rotating 180 degrees (complete turnaround).

Question 40

A balanced reciprocal translocation involves

Accepted Answer

Exchange with no net gain or loss of genetic material — Balanced reciprocal translocations involve exchange of chromosomal material between two chromosomes with no net gain or loss of genetic material, potentially causing problems during meiosis.

Question 41

Which best describes complex multigenic disorders?

Accepted Answer

Caused by interactions between gene variants and environmental factors — Complex multigenic (or multifactorial/polygenic) disorders are caused by interactions between variant forms of genes and environmental factors.

Question 42

Anaphase lag can lead to aneuploidy through

Accepted Answer

Failure of pairing followed by random assortment — Failure of pairing of homologous chromosomes followed by random assortment (anaphase lag) can lead to aneuploidy, in addition to nondisjunction.

Question 43

Mosaicism affecting which chromosomes is most common?

Accepted Answer

Sex chromosomes — Mosaicism affecting sex chromosomes is common, whereas autosomal mosaicism is relatively uncommon.

Question 44

In most chromosomal disorders, the parents are

Accepted Answer

Normal with de novo changes in offspring — In most cases, chromosomal disorders result from de novo changes (parents are normal and risk of recurrence in siblings is low), with translocation Down syndrome being an important exception.

Question 45

Fertilization of a gamete with an extra chromosome (n+1) by a normal gamete produces

Accepted Answer

Trisomic zygote (2n+1) — Fertilization of a gamete containing an extra chromosome (n+1) by a normal gamete (n) results in a trisomic zygote with 2n+1 chromosomes.

Question 46

Polyploidy (3n, 4n) generally results in

Accepted Answer

Spontaneous abortion — Polyploidy, where chromosome numbers are 3n or 4n (exact multiples of the haploid number other than 2n), generally results in spontaneous abortion.

Question 47

Which THREE autosomal trisomies were among the first chromosomal abnormalities identified?

Accepted Answer

13, 18, and 21 — Trisomies 21, 18, and 13 were among the first chromosomal abnormalities identified, along with cri du chat syndrome (5p deletion).

Question 48

The incidence of Down syndrome in women younger than 20 years is approximately

Accepted Answer

1 in 1550 live births — Down syndrome occurs in approximately 1 in 1550 live births in women younger than 20 years, increasing dramatically to 1 in 25 in women older than 45 years.

Question 49

The immune dysfunction in Down syndrome primarily affects

Accepted Answer

Mainly T cell function — Patients with Down syndrome demonstrate abnormal immune responses with abnormalities affecting mainly T cell functions, predisposing to infections and thyroid autoimmunity.

Question 50

In the translocation form of Down syndrome, the translocated chromosome is most commonly inherited from

Accepted Answer

A parent who is a carrier of a robertsonian translocation — The translocation form is frequently (but not always) familial, with the translocated chromosome inherited from a parent who is typically a carrier of a robertsonian translocation.

Genetic Disorders MCQ Examination (Part 2) | MCQ Quiz | OmpathStudy Kenya

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