Variations of homologous genes that result in differences in structure and function are

Alleles

Explanation:

The variation in the homologous genes that result in different structure and function is known as allele. They represent the different forms of genes one is dominant and one is recessive.

The expression of characters by both the genes are different. Example: If T represents tallness then t represents dwarfness.

The homologous pair TT represents tallness and the other allele on the same gene is tt which shows dwarfness.

it creates acid rain