Question 1

Which of the following best describes the difference between aneuploidy and polyploidy?

Accepted Answer

Aneuploidy is the gain or loss of one or more chromosomes but not a complete set, while polyploidy is the presence of more than two complete haploid sets of chromosomes.

Question 2

A human karyotype is described as 47,XXY. Which syndrome does this represent, and what is the underlying chromosomal event?

Accepted Answer

Klinefelter syndrome; trisomy of the X chromosome due to nondisjunction

Question 3

Which of the following best explains why monosomy for most human autosomes is lethal?

Accepted Answer

Monosomy unmasks recessive lethal alleles and may result in haploinsufficiency, where a single copy of a gene is insufficient for normal function.

Question 4

A plant geneticist observes a maize plant with 21 chromosomes, while the normal diploid number is 20. What is the most likely chromosomal condition of this plant?

Accepted Answer

Trisomy

Question 5

Which of the following statements about Down syndrome (trisomy 21) is CORRECT?

Accepted Answer

The majority of cases are due to nondisjunction during maternal meiosis I.

Question 6

A woman aged 42 is pregnant. What is the approximate risk of her child being born with Down syndrome compared to a woman aged 30, and what is the biological explanation?

Accepted Answer

The risk is about ten times higher due to increased duration of meiotic arrest in oocytes, which may increase nondisjunction events.

Question 7

Which of the following best describes a terminal deletion?

Accepted Answer

A deletion that removes a segment from the end of a chromosome.

Question 8

Cri du chat syndrome is caused by which specific chromosomal aberration?

Accepted Answer

A terminal deletion of the short arm of chromosome 5

Question 9

Which of the following is a likely consequence of a paracentric inversion heterozygote undergoing a single crossover within the inversion loop during meiosis?

Accepted Answer

Formation of one dicentric and one acentric chromatid, both with duplications and deletions

Question 10

Which of the following best explains the evolutionary significance of gene duplication?

Accepted Answer

Duplicated genes can accumulate mutations and potentially evolve new functions, increasing genetic diversity.

Question 11

A Drosophila fly with the Bar-eye phenotype is found to have a duplication of region 16A on the X chromosome. Which genetic mechanism most likely produced this duplication?

Accepted Answer

Unequal crossing over during meiosis

Question 12

Copy number variations (CNVs) are significant in human genetics because:

Accepted Answer

They can influence disease susceptibility and normal traits by altering the number of gene copies.

Question 13

Which of the following is TRUE regarding reciprocal translocations?

Accepted Answer

They involve the exchange of segments between nonhomologous chromosomes and may produce genetically unbalanced gametes.

Question 14

Familial Down syndrome is most often caused by which chromosomal event?

Accepted Answer

A Robertsonian translocation between chromosomes 14 and 21

Question 15

In a reciprocal translocation heterozygote, what is the expected outcome of alternate segregation during meiosis?

Accepted Answer

Gametes will be either normal or balanced for the translocation, containing a complete set of genetic information.

Question 16

Which of the following best describes the effect of a pericentric inversion?

Accepted Answer

It involves a chromosome segment that includes the centromere.

Question 17

A genetic counselor is advising a couple where one parent is a carrier of a balanced Robertsonian translocation involving chromosomes 14 and 21. What is the probability that a gamete from this parent will contain two copies of chromosome 21 (one normal and one translocated), potentially leading to Down syndrome after fertilization with a normal gamete?

Accepted Answer

$$\frac{1}{4}$$

Question 18

Which of the following is a likely evolutionary advantage of inversions in a population?

Accepted Answer

They preserve favorable combinations of alleles by suppressing crossing over within the inverted region.

Question 19

A patient is found to have a higher-than-average copy number of the CCL3L1 gene. Which of the following is a likely consequence?

Accepted Answer

Suppression of HIV progression and slower development of AIDS

Question 20

Which of the following best explains why individuals with Down syndrome have a decreased risk of developing certain solid tumors?

Accepted Answer

They have an extra copy of the DSCR1 gene, which suppresses VEGF and inhibits angiogenesis.

Chromosome Mutations: Variation in Number and Arrangement

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