IB Biology Exam Prep

Category - Biology

Polyploidy in an organism is most likely to result from a:
  1. Frameshift mutation that deletes a termination codon.
  2. Low level of helicase activity during DNA replication.
  3. Reciprocal exchange of material between nonsister chromatids.
  4. Chromosomal nondisjunction during meiosis.
Explanation
Correct Response: D. When an organism is polyploid, the organism has more chromosomes than the normal number in a set for that species. This occurs during meiosis after the DNA has been replicated. It results from a failure of chromosomes to segregate into separate daughter cells. Frameshift mutations that delete a termination codon most frequently result in nonfunctional proteins as the result of the incorporation of extra amino acids (A). Helicase is an enzyme that separates the strands of DNA molecules. Low helicase activity potentially slows down DNA replication but would not result in polyploidy (B). During a reciprocal exchange of material between nonsister chromatids (C), DNA is neither lost nor gained, so this process does not result in polyploidy.
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