The genes of the multicellular eukaryotes often contain many transposable elements. But most of these elements do not affect the expression of the gene because with regard to gene function they are inserted into non-coding sequences, such as introns.
Hence, the messenger Ribonucleic acid (mRNA) produced by this gene will not include any sequences from transposable elements, because they had been spliced out of the pre-mRNA with the surrounding intron.
Presumably, transposable elements insert into both exons and introns but only the insertions into introns will remain in the population because they are less likely to cause deleterious mutations. Insertions into exons are said to be subjected to negative selection.
Humans as well as other multicellular organisms can survive with much mobile DNA in the genome because the vast majority is inactive and cannot move or increase in copy number.