At Cambridge University, James Watson, Francis Crick and Rosalind Franklin discover the “double-helix” structure of DNA.

DNA is found in the nucleus of every human cell and determines the biological traits that are passed to future generations.

The Apgar scale is named for Dr. Virginia Apgar, who develops a test to evaluate the health of newborns.

The scale measures a baby’s heart rate, breathing, muscle tone, reflexes and color. The test tells doctors whether a newborn needs emergency help.