For Each of the Following Sentences, Fill in the Blanks

Essay

For each of the following sentences, fill in the blanks with the best word or phrase in the list below.Not all words or phrases will be used; use each word or phrase only once.
$\begin{array}{llcc} \text { divergence } & \text { purifying selection } \\ \text { exon shuffling} & \text { single-nucleotide polymorphisms }\\ \text {gene duplication } & \text {synteny }\\ \text { horizontal gene transfer } & \text { unequal crossing-over }\\\end{array}$


__________ may arise by recombination within introns and can create proteins with novel combinations of domains.Scientists and government regulators must be very careful when introducing herbicide-resistant transgenic corn plants into the environment, because if resistant weeds arise from __________, then the herbicides could become useless.Families of related genes can arise from a single ancestral copy by __________ and subsequent __________.