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 cytogeneticist is analyzing a karyotype and observes a chromosome with the centromere located very close to one end, resulting in a very short p arm and a long q arm. What is the correct classification for this chromosome shape?

Accepted Answer

Acrocentric

Question 3

A plant breeder crosses a diploid (2n) plant with a tetraploid (4n) plant. What is the expected chromosome number in the resulting triploid offspring, and what is a likely consequence for fertility?

Accepted Answer

The offspring will have $$3n$$ chromosomes and will likely be infertile due to unbalanced gamete formation during meiosis.

Question 4

Which of the following statements about nondisjunction is correct?

Accepted Answer

Nondisjunction during meiosis I results in all gametes being aneuploid, while nondisjunction during meiosis II results in two normal and two abnormal gametes.

Question 5

A patient is diagnosed with Turner syndrome. Which of the following genetic mechanisms is responsible for the symptoms observed in this syndrome?

Accepted Answer

Monosomy of the X chromosome resulting in haploinsufficiency of the SHOX gene.

Question 6

Which molecular technique would be most appropriate to detect a microdeletion that is too small to be seen by standard chromosome banding?

Accepted Answer

Fluorescent in situ hybridization (FISH)

Question 7

A reciprocal balanced translocation heterozygote undergoes meiosis. Which segregation pattern will produce gametes with a full haploid set of genes?

Accepted Answer

Alternate segregation

Question 8

In a paracentric inversion heterozygote, what is the likely outcome of a single crossover event within the inversion loop during meiosis?

Accepted Answer

Formation of a dicentric chromosome and an acentric fragment, both of which are typically inviable.

Question 9

A geneticist observes a human karyotype with 45 chromosomes, including a large chromosome formed by the fusion of two acrocentric chromosomes. What is the most likely explanation for this observation?

Accepted Answer

Robertsonian translocation

Question 10

Which of the following best explains why trisomy 21 (Down syndrome) is more common in children born to older mothers?

Accepted Answer

Older mothers have a higher rate of meiotic nondisjunction during oogenesis, increasing the risk of aneuploid gametes.

Question 11

Which of the following is a direct consequence of unequal crossover between homologous chromosomes during meiosis?

Accepted Answer

Partial duplication on one homolog and partial deletion on the other.

Question 12

A scientist is studying the chromatin structure of a eukaryotic cell. Which of the following correctly describes the organization of nucleosomes and higher-order chromatin structure?

Accepted Answer

The 10-nm fiber coils into a 30-nm solenoid structure, stabilized by histone H1.

Question 13

Which of the following best explains why polyploidy is more common and better tolerated in plants than in animals?

Accepted Answer

Plants are less sensitive to changes in gene dosage and can often survive with extra sets of chromosomes.

Question 14

During DNA replication, how are nucleosomes reassembled on the newly synthesized DNA?

Accepted Answer

Old H3-H4 tetramers are randomly distributed to daughter strands, while H2A-H2B dimers are reassembled from both old and new histones.

Question 15

A patient presents with a syndrome caused by an interstitial deletion on chromosome 11, resulting in the loss of multiple genes. Which of the following is the most likely mechanism for this chromosomal abnormality?

Accepted Answer

Two chromosome breaks with loss of the intervening segment.

Question 16

Which of the following is a key feature of chromosome territories during interphase?

Accepted Answer

Each chromosome occupies a specific region, and larger, gene-rich chromosomes are generally near the center of the nucleus.

Question 17

A cytogeneticist uses Giemsa banding to analyze a patient's chromosomes. What information can be obtained from this technique?

Accepted Answer

The size, shape, and banding pattern of each chromosome, allowing identification of structural abnormalities.

Question 18

Which of the following best describes the genetic consequences of alternate versus adjacent segregation in a reciprocal balanced translocation heterozygote?

Accepted Answer

Alternate segregation produces gametes with a full haploid set of genes, while adjacent segregation produces gametes with duplications and deletions.

10-2. Eukaryotic Chromosome Abnormalities and Molecular Organization

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