Question

the different versions of a gene (often expressed as letter symbols)
recessive
sexual reproduction
allele
dominant allele

Explanation:

The question is about matching the definition "the different versions of a gene (often expressed as letter symbols)" to the correct term. The term "allele" is defined as the different forms of a gene. "Recessive" and "Dominant Allele" refer to types of alleles, and "sexual reproduction" is a mode of reproduction, not related to gene versions. So the correct term is "allele".

Answer:

allele