Crossing over between nonsister chromatids during meiosis is significant in heredity. this process most likely leads to an increase in which of the following?
a. the expression of dominant traits
b. number of gametes
c. the occurrence of polyploidy
d. genetic variation

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The crossing over is a process where the chromatids pair and exchange sections of DNA, which lead to exchange genes (this result is call genetic recombination). So, the crossing over between nonsister chromatids during meiosis is significant in heredity because it leads to an increase of genetic variation (answer d.)