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Difficulty: HardGene Mutations and Chromosomal Aberrations

During a plant breeding experiment, a researcher treats dividing meristematic cells of a diploid crop species (2n=142n = 14) with the chemical mutagen colchicine. Colchicine inhibits microtubule polymerization and prevents the assembly of the mitotic spindle apparatus during cell division, preventing chromatid separation into daughter nuclei. Which of the following correctly describes the chromosome count and the class of mutation present in the resulting cells?

  1. 28 chromosomes, resulting from polyploidy which is a chromosomal aberrationAnswer
  2. B
    15 chromosomes, resulting from aneuploidy which is a chromosomal aberration
  3. C
    28 chromosomes, resulting from a frameshift gene mutation
  4. D
    14 chromosomes, resulting from a point substitution gene mutation

Answer

28 chromosomes, resulting from polyploidy which is a chromosomal aberration
Colchicine interferes with microtubule assembly, disabling spindle fibers during mitosis. As a result, duplicated sister chromatids are retained within a single cell nucleus instead of being pulled to opposite poles. For an initial diploid cell (2n=142n = 14), this failure of segregation results in tetraploidy (4n=284n = 28). Because this change involves entire sets of chromosomes rather than alterations within single nucleotide chains, it is classified as a numerical chromosomal aberration (polyploidy).

Step-by-Step Solution

1
Analyze the action of colchicine on dividing cells
Colchicine prevents spindle fiber formation, blocking anaphase separation of sister chromatids.
Microtubules cannot assemble, so duplicated chromosomes remain together in a single nucleus without cytokinesis.
2
Calculate the resulting chromosome number
The diploid number 2n=142n = 14 is doubled to 4n=284n = 28.
Since DNA replication occurred before mitosis and sister chromatids failed to segregate into separate daughter cells, the chromosome set doubles.
3
Classify the type of genetic mutation
Numerical doubling of whole chromosome sets is classified as polyploidy, a major chromosomal aberration.
Gene mutations affect nucleotide sequences within individual genes, whereas numerical alterations of whole chromosome sets are chromosomal aberrations.

Key Concept

Polyploidy and Numerical Chromosomal Aberrations
Estimated Time:1m 30s
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Topics

Gene Mutations and Chromosomal Aberrations

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