Genetic testing had its origins in the 1950s when scientists discovered that an additional copy of chromosome 21 causes Trisomy 21, also known as Down syndrome. Methods for staining chromosomes were used to sort and count chromosomes, a process called karyotyping. That process, combined with the ability to collect fetal cells from a pregnant woman’s amniotic fluid, provided scientists the ability to conduct genetic prenatal screening. Such testing revealed DNA-based diagnoses of genetic disorders caused by biologic irregularities such as too many chromosomes, too few, or clusters of chromosomes in the wrong places. As genetic testing became widespread, scientists began researching the substance of DNA, the chemical structure deciphered in 1953 by Rosalind Franklin, James Watson, and Francis Crick. Over the next several decades, it was discovered that helix-shaped patterns of paired chemical bases — adenine, thymine, cytosine, and guanine — provided a code that cells would decode into amino acids, the building blocks of protein. Scientists also discovered through research into the human genome that approximately 98% of DNA doesn’t actually code for proteins, and was seen as “junk DNA.”
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