98% of your DNA is useless junk
Not wrong, but our understanding became significantly more precise.
TaughtOnly about 2% of the genome codes for proteins. The rest is evolutionary debris: junk DNA with no function.
NowMuch of the noncoding genome regulates when and where genes switch on. The ENCODE project reported in 2012 that most of the genome is biochemically active, though how much is genuinely functional is still fiercely argued.
What actually happened
This entry is tagged "refined" rather than "disproved" on purpose, because the loud version of this story is itself an overcorrection. ENCODE's 2012 headline claim that 80% of the genome is functional was widely criticized by evolutionary biologists, who pointed out that "a protein binds here sometimes" is a very low bar for calling something functional, and that comparative genomics suggests a much smaller fraction is under selection.
What is solid: the noncoding genome is not inert. It contains promoters, enhancers, silencers, insulators, genes for functional RNAs that never become proteins, and the regulatory machinery that explains how 20,000 genes build something as complicated as you. The blunt classroom line that 98% of your DNA is garbage is dead. The precise replacement is still being negotiated, and anyone who tells you the fraction with certainty is overselling.
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Who was taught this
Still standard through 2013, so anyone who finished school between 1950 and 2012 learned the earlier version.