The biological significance of crossing over is that it
- A. keeps linkage groups permanently intact
- B. halves the chromosome number of the gametes
- C. ensures that all gametes are genetically identical
- D. produces new combinations of alleles on the same chromosome
Explanation
Exchange between non sister chromatids creates chromosomes carrying combinations of alleles that neither parent had, and this recombination is a major source of the variation natural selection works on. Halving the chromosome number is the job of the reduction division itself, not of crossing over. Crossing over does the opposite of keeping linkage groups intact, since it breaks linkage up.
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