Question 1

Which of the following best describes aneuploidy?

Accepted Answer

An organism gains or loses one or more chromosomes, but not a complete set.

Question 2

A child is born with the karyotype $$47, 21+$$ and exhibits a flat face, short stature, and poor muscle tone. Which chromosomal event most likely led to this condition?

Accepted Answer

Nondisjunction during meiosis resulting in trisomy 21.

Question 3

Which equation correctly represents monosomy in a diploid organism?

Accepted Answer

$$2n - 1$$

Question 4

In plants, trisomics for longer chromosomes tend to grow slower and show altered leaf, stem, and grain morphology. What is the most likely explanation for this phenomenon?

Accepted Answer

Gene dosage imbalance caused by the extra chromosome affects normal development.

Question 5

Which chromosomal aberration is most likely to result in a compensation loop during synapsis?

Accepted Answer

Intercalary deletion

Question 6

A patient exhibits intellectual disability, delayed development, and a distinctive cat-like cry. Cytogenetic analysis reveals a segmental deletion on chromosome 5. What syndrome does this patient most likely have?

Accepted Answer

Cri du chat syndrome

Question 7

Which of the following statements about gene duplication is FALSE?

Accepted Answer

Duplicated genes always produce identical gene products.

Question 8

The Bar mutation in Drosophila is an example of which chromosomal aberration, and what is its effect?

Accepted Answer

Duplication; it causes narrow, slit-like eyes due to increased gene dosage.

Question 9

Which chromosomal aberration involves the rearrangement of a segment within the same chromosome, requiring two breaks and reinsertion of the segment in reverse orientation?

Accepted Answer

Inversion

Question 10

During meiosis, a single crossover within a paracentric inversion loop produces which two types of abnormal chromatids?

Accepted Answer

Dicentric and acentric chromatids

Question 11

Which of the following best describes a reciprocal translocation?

Accepted Answer

Exchange of segments between two nonhomologous chromosomes without loss or gain of genetic material.

Question 12

In familial Down syndrome, which chromosomal event is responsible for the inheritance of the disorder?

Accepted Answer

Robertsonian translocation between chromosomes 14 and 21

Question 13

Which equation represents trisomy in a diploid organism?

Accepted Answer

$$2n + 1$$

Question 14

A genetic counselor recommends amniocentesis for a pregnant woman over 45 years old. What is the primary reason for this recommendation?

Accepted Answer

Increased risk of chromosomal abnormalities such as Down syndrome with maternal age.

Question 15

Which chromosomal aberration is most likely to result in semisterility due to the production of genetically unbalanced gametes?

Accepted Answer

Reciprocal translocation

Question 16

Fragile-X syndrome is associated with which molecular feature?

Accepted Answer

Trinucleotide repeat expansion of CGG in the FMR1 gene

Question 17

Which of the following is TRUE regarding copy number variants (CNVs)?

Accepted Answer

CNVs can be associated with both positive and negative effects on disease risk.

Question 18

Which chromosomal aberration is most likely to be tolerated in plants but not in animals, and why?

Accepted Answer

Monosomy; plants can often survive with a single chromosome loss, but animals usually cannot due to haploinsufficiency.

Question 19

Which of the following best explains the evolutionary advantage of inversions?

Accepted Answer

Inversions can preserve alleles from generation to generation by suppressing recombination.

Question 20

A cytogenetic analysis reveals a gap on the X chromosome in a male patient with intellectual disability. Which condition is most likely present, and what is the underlying genetic cause?

Accepted Answer

Fragile-X syndrome; caused by expansion of CGG repeats in the FMR1 gene.

Chromosome Mutations: Variation in Number and Arrangement

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