Biology Inheritance / Variation & Genetics AJK 2019
PMDC Verified Question 79 of 94
During crossing over, exchange of segments takes place between:
A
Sister chromatids of homologous chromosomes
B
Non-sister chromatids of homologous chromosomes
C
Non-sister chromatids of non-homologous chromosomes
D
Sister chromatids of non-homologous chromosome
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Non-sister chromatids of homologous chromosomes
Concept:

Recombination requires the physical exchange of genetic material between paternal and maternal DNA sequences.

Solution:

  • During Prophase I of meiosis, homologous chromosomes pair up to form bivalents.
  • Crossing over specifically occurs between the non-sister chromatids of these homologous chromosomes.
  • One chromatid from the maternal chromosome exchanges equivalent segments with a chromatid from the paternal chromosome, introducing genetic diversity.


Why other options are incorrect:

  • Sister chromatids: Exchanging segments between identical sister chromatids would yield no genetic variation.
  • Non-homologous chromosomes: An exchange here represents a deleterious chromosomal mutation known as a translocation, not natural crossing over.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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