This study investigates the polyadenylation of mRNA in human and mouse genes, focusing on the distribution and characteristics of polyadenylation sites. The researchers surveyed genome regions containing cleavage sites, known as poly(A) sites, for 13,942 human and 11,155 mouse genes. They found that a significant proportion of these genes exhibit alternative polyadenylation, with ~54% of human genes and ~32% of mouse genes having multiple poly(A) sites. The conservation of polyadenylation configurations between human and mouse orthologs is statistically significant, indicating that alternative polyadenylation is a widely used mechanism for producing alternative gene transcripts in these species. The study also reveals that genes with different functional annotations show biases in their polyadenylation configurations. Many poly(A) sites contain multiple cleavage sites, leading to heterogeneous 3′ end formation, suggesting that the polyadenylation process is imprecise. Different types of poly(A) sites have distinct nucleotide compositions in surrounding genomic regions, providing insights into the mechanisms of polyadenylation and gene expression regulation.This study investigates the polyadenylation of mRNA in human and mouse genes, focusing on the distribution and characteristics of polyadenylation sites. The researchers surveyed genome regions containing cleavage sites, known as poly(A) sites, for 13,942 human and 11,155 mouse genes. They found that a significant proportion of these genes exhibit alternative polyadenylation, with ~54% of human genes and ~32% of mouse genes having multiple poly(A) sites. The conservation of polyadenylation configurations between human and mouse orthologs is statistically significant, indicating that alternative polyadenylation is a widely used mechanism for producing alternative gene transcripts in these species. The study also reveals that genes with different functional annotations show biases in their polyadenylation configurations. Many poly(A) sites contain multiple cleavage sites, leading to heterogeneous 3′ end formation, suggesting that the polyadenylation process is imprecise. Different types of poly(A) sites have distinct nucleotide compositions in surrounding genomic regions, providing insights into the mechanisms of polyadenylation and gene expression regulation.