What is the impact of selection on orthologous and paralogous genes? How would this impact differ in different regions of protein coding genes?

Exactly . Paralogs and orthologs , both go under natural selection. But harmful mutations tend to have a less fatal effect if they happen to paralogs as there would be a backup for the malfunctioning protein. In paralogs, if a bad mutation happens to a protein, the paralogous protein will compensate and help the organism maintain its function but in orthologs one mistake is enough to do harm because there are no other proteins to perform the function of the wild protein.

All the different members of the tubulin family of genes (and proteins) are sufficiently similar in sequence to suggest a common ancestral sequence. Thus all these sequences are considered to be homologous. More specifically, sequences that presumably diverged as a result of gene duplication (e.g., the α- and β-tubulin sequences) are described as paralogous. Sequences that arose because of speciation (e.g., the α-tubulin genes in different species) are described as orthologous

Reference : Molecular Cell Biology of Lodish et al 8th edition page 325

Also see Campbell Biology 9th edition chapter 26 section 26-4