The proteins encoded by genes within the same gene family have modularity if structure because : ( D ) gene families usually have similar DNA sequences and therefore similar protein structure.
A gene family is a set of similar genes that is formed by the duplication of single original gene, which has a similar biochemical function. natural selection affects the increase or decrease of a gene family.
Gene families have similar DNA sequence because the genes found in a gene family is from an ancestral gene, also their protein structure is similar
Hence we can conclude that gene families usually have similar DNA sequences and therefore similar protein structure.