Question 1

Which of the following best describes the difference between euchromatin and heterochromatin in eukaryotic chromosomes?

Accepted Answer

Euchromatin is less condensed and contains actively expressed genes, while heterochromatin is tightly condensed and contains fewer expressed genes.

Question 2

A human cell with 45 chromosomes is most likely an example of which condition?

Accepted Answer

Aneuploidy

Question 3

Which mechanism can lead to the formation of a triploid (3n) plant?

Accepted Answer

Fusion of a diploid gamete and a haploid gamete ($2n + n$)

Question 4

Which of the following is a consequence of odd-numbered polyploidy (e.g., $3n$, $5n$) in plants?

Accepted Answer

Decreased fertility due to nonviable gametes

Question 5

A patient is diagnosed with Prader-Willi syndrome. Genetic analysis reveals both copies of chromosome 15 are inherited from the mother. What is this phenomenon called?

Accepted Answer

Uniparental disomy

Question 6

Which type of chromosomal abnormality is most commonly observed in newborn humans?

Accepted Answer

Autosomal trisomy of chromosomes 13, 18, or 21

Question 7

During meiosis I, if homologous chromosomes fail to separate, what types of gametes are produced?

Accepted Answer

Gametes with $n+1$ and $n-1$ chromosomes

Question 8

Which chromosomal rearrangement involves the fusion of two nonhomologous chromosomes?

Accepted Answer

Robertsonian translocation

Question 9

A chromosome with its centromere located near the end, resulting in a very short p arm and a long q arm, is classified as:

Accepted Answer

Acrocentric

Question 10

Which of the following best explains why polyploidy is often used in agriculture to produce seedless fruit varieties?

Accepted Answer

Odd-numbered polyploids (e.g., $3n$) have decreased fertility, resulting in nonviable gametes and seedless fruits.

Question 11

Which chromatin structure is observed as 'beads-on-a-string' under electron microscopy?

Accepted Answer

10-nm fiber

Question 12

A geneticist observes a patient with a deletion of a small region on chromosome 11, resulting in a combination of Wilms tumor, aniridia, genitourinary anomalies, and mental retardation. What is the most likely diagnosis?

Accepted Answer

WAGR syndrome

Question 13

Which of the following statements about chromosome territories in the nucleus is correct?

Accepted Answer

Once confined to a territory, a chromosome does not leave until M phase is initiated.

Question 14

Which of the following is a direct result of mitotic nondisjunction early in embryogenesis?

Accepted Answer

Mosaicism

Question 15

Which of the following is true regarding the organization of histone proteins in a nucleosome?

Accepted Answer

A nucleosome core particle contains two molecules each of H2A, H2B, H3, and H4.

Question 16

A geneticist is mapping the position of a gene using deletion mapping. Which phenomenon allows a recessive allele to be expressed when the dominant allele is deleted?

Accepted Answer

Pseudodominance

Question 17

Which of the following chromosomal rearrangements is most likely to result in crossover suppression during meiosis?

Accepted Answer

Inversion

Question 18

A plant breeder crosses a diploid ($2n$) egg with a diploid ($2n$) pollen. What is the chromosome number of the resulting offspring?

Accepted Answer

$4n$

Question 19

Which of the following is a function of higher-order chromatin condensation in eukaryotic cells?

Accepted Answer

It allows for efficient separation of chromosomes at anaphase and regulates gene expression.

Eukaryotic Chromosome Abnormalities and Molecular Organization: Study Notes

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