Question 1

Which of the following best describes the difference between metacentric and acrocentric chromosomes?

Accepted Answer

Metacentric chromosomes have the centromere near the middle, resulting in arms of equal length, while acrocentric chromosomes have the centromere close to one end, producing a very short p arm and a long q arm.

Question 2

A human cell with 47 chromosomes, including three copies of chromosome 21, is best described as:

Accepted Answer

Aneuploid, specifically trisomic for chromosome 21

Question 3

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

Accepted Answer

Fluorescent in situ hybridization (FISH)

Question 4

A plant breeder crosses a diploid (2n) plant with a tetraploid (4n) plant. What is the expected chromosome number in the resulting hybrid offspring?

Accepted Answer

$$3n$$

Question 5

Which of the following is a consequence of a Robertsonian translocation?

Accepted Answer

The chromosome number is reduced by two, but most genetic material is retained.

Question 6

In a reciprocal balanced translocation heterozygote, which segregation pattern during meiosis produces viable gametes with a full haploid set of genes?

Accepted Answer

Alternate segregation

Question 7

Which syndrome is caused by a terminal deletion of the short arm of chromosome 5?

Accepted Answer

Cri-du-chat syndrome

Question 8

What is the primary reason that most animals are highly sensitive to aneuploidy, while many plants tolerate it better?

Accepted Answer

Animals are more sensitive to gene dosage imbalances than plants.

Question 9

A fruit fly (Drosophila melanogaster) has a diploid chromosome number of 8. If a nondisjunction event during meiosis I produces a gamete with 5 chromosomes, what is the chromosome number of the resulting zygote after fertilization with a normal gamete?

Accepted Answer

$$2n + 1 = 9$$

Question 10

Which of the following best explains the phenomenon of position effect variegation (PEV) in Drosophila?

Accepted Answer

Gene expression is altered when a gene is relocated near heterochromatin, leading to variable silencing.

Question 11

Which histone protein is primarily associated with stabilizing the solenoid (30-nm fiber) structure of chromatin?

Accepted Answer

H1

Question 12

A patient is diagnosed with Turner syndrome. Which karyotype would you expect to find in her cells?

Accepted Answer

45, X

Question 13

Which of the following is a likely outcome of crossing over within a paracentric inversion loop during meiosis?

Accepted Answer

Formation of a dicentric chromosome and an acentric fragment, both leading to inviable gametes

Question 14

Which of the following best describes the composition of a nucleosome core particle?

Accepted Answer

An octamer of histones: two each of H2A, H2B, H3, and H4, wrapped by about 146 bp of DNA

Question 15

A trisomic jimson weed plant (2n = 24 + 1) displays a unique fruit phenotype compared to the wild type. What is the most likely explanation for this phenotypic difference?

Accepted Answer

Altered gene dosage from the extra chromosome leads to an imbalance in gene products.

Question 16

Which of the following statements about polyploidy is correct?

Accepted Answer

Polyploidy can result in increased fruit size and hybrid vigor in plants.

Question 17

Which chromosomal abnormality is most commonly associated with spontaneous abortion in humans?

Accepted Answer

Aneuploidy (abnormal chromosome number)

Question 18

What is the effect of a deletion that unmasks a recessive allele on the homologous chromosome?

Accepted Answer

Pseudodominance, where the recessive phenotype is expressed

Question 19

Which of the following best explains why alternate segregation in reciprocal balanced translocation heterozygotes leads to fertility, while adjacent segregation does not?

Accepted Answer

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

Chromosome Structure, Number, and Variation in Eukaryotes

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