Given below are a few statements related to inheritance biology:
A. A crossover is the breakage of two DNA molecules at the same position and their rejoining in two reciprocal recombinant combinations.
B. Crossing over takes place at the four-chromatid stage.
C. As the distance between two genes increases, the recombination frequencies move closer to 50%.
D. Percentage of recombinants between two genes can be used as a quantitative index of the accurate physical distance between them.
Which one of the following options is a combination of all correct statements?

Correct option is C

Correct Answer:
Option (3) – A, B and C
Explanation:
A is correct: A crossover involves reciprocal exchange between homologous chromatids at corresponding positions.
B is correct: Crossing over occurs during pachytene of prophase I, when four chromatids are present.
C is correct: With increasing distance between genes, multiple crossovers occur and recombination frequency approaches a maximum of 50%.
D is incorrect: Recombination frequency reflects genetic distance, not the accurate physical distance, and it saturates at 50%.
Information Booster :
· Genetic maps are based on recombination frequencies, not actual base-pair distances.
· Multiple crossovers can mask true physical separation between genes.
· Recombination frequency cannot exceed 50%, even for genes far apart.
· Physical mapping requires molecular techniques such as sequencing.
Additional Information (Incorrect Options):
Option 1: Incomplete because B is also correct.
Option 2: Incorrect due to inclusion of statement D.
Option 4: Incorrect because statement D is false.