Question 1

Which of the following best describes the process and consequence of X-chromosome inactivation in human females?

Accepted Answer

One X chromosome is randomly inactivated in each somatic cell, resulting in genetic mosaicism and dosage compensation.

Question 2

A karyotype is most useful for which of the following purposes?

Accepted Answer

Examining chromosome number and detecting major structural abnormalities.

Question 3

Which chromosome classification is correct based on centromere position?

Accepted Answer

Acrocentric chromosomes have their centromere close to one end, resulting in a very short p arm.

Question 4

A female cat heterozygous for orange and black coat-color alleles displays patches of both colors. What genetic mechanism explains this phenomenon?

Accepted Answer

X-chromosome inactivation leading to mosaic expression of X-linked alleles.

Question 5

Which region of the Y chromosome is responsible for male development, and what is its function?

Accepted Answer

SRY gene; encodes the testis-determining factor.

Question 6

Why are Y-chromosome haplotypes particularly useful for tracing paternal lineages in human populations?

Accepted Answer

Because most of the Y chromosome does not recombine, haplotypes are transmitted largely intact from father to son.

Question 7

Which of the following best distinguishes euploidy from aneuploidy?

Accepted Answer

Euploidy retains balanced gene dosage relationships, while aneuploidy disturbs gene dosage by affecting individual chromosomes.

Question 8

A child is diagnosed with Down syndrome. Which chromosomal abnormality is most commonly responsible for this condition?

Accepted Answer

Trisomy 21

Question 9

During meiosis in a trisomic individual, what abnormal pairing configuration can occur, and what is its consequence?

Accepted Answer

A trivalent forms, leading to unequal chromosome segregation and gametes with abnormal chromosome numbers.

Question 10

Sex-chromosome aneuploidies often produce less severe effects than autosomal aneuploidies. Which principle explains this difference?

Accepted Answer

The single-active-X principle and the small number of genes on the Y chromosome.

Question 11

Which syndrome is associated with the karyotype $$47, XXY$$?

Accepted Answer

Klinefelter syndrome

Question 12

Nondisjunction during meiosis can result in which of the following outcomes?

Accepted Answer

Gametes with abnormal chromosome numbers, such as monosomy or trisomy.

Question 13

A chromosome deletion can be used experimentally for gene mapping. Which principle allows this?

Accepted Answer

If a recessive allele becomes phenotypically visible when the corresponding region on the homologous chromosome is deleted, the allele must lie within the deleted region.

Question 14

Unequal crossing-over between red and green pigment genes on the X chromosome can result in which of the following?

Accepted Answer

Formation of a chimeric gene, deletions causing color blindness, and duplications of pigment genes.

Question 15

What is the consequence of crossing-over within a paracentric inversion loop during meiosis?

Accepted Answer

Production of acentric and dicentric chromosomes, which are structurally abnormal.

Question 16

A reciprocal translocation heterozygote produces a quadrivalent during meiosis. Which segregation pattern results in balanced gametes?

Accepted Answer

Alternate segregation, where normal chromosomes migrate to one pole and translocated chromosomes to the other.

Question 17

A Robertsonian translocation involving chromosome 21 can result in which genetic outcome?

Accepted Answer

Inherited form of Down syndrome due to abnormal chromosome-21 material.

Question 18

Which of the following best describes the difference between autopolyploidy and allopolyploidy?

Accepted Answer

Autopolyploids contain chromosome sets from a single species; allopolyploids contain sets from two or more different species.

Question 19

Despite large differences in genome size among cereal grasses, what feature remains evolutionarily conserved?

Accepted Answer

Synteny groups, which are conserved chromosomal regions with similar gene linkages.

Question 20

Which equation correctly represents the chromosome number in a human diploid cell?

Accepted Answer

$$2n = 46$$

Human Chromosomes and Chromosome Behavior: Structure, Variation, and Genetic Consequences

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