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More than 60 years ago, Francis Crick and James Watson discovered the double-helical structure of deoxyribonucleic acid—better known as DNA. Today, for the cost of a Netflix subscription, you can have your DNA sequenced to learn about your ancestry and proclivities. Yet, while it is an irrefutable fact that the transmission of DNA from parents to offspring is the biological basis for heredity, we still know relatively little about the specific genes that make us who we are.

That is changing rapidly through genome-wide association studies—GWAS, for short. These studies search for differences in people’s genetic makeup—their “genotypes”—that correlate with differences in their observable traits—their “phenotypes.” In a GWAS recently published in Nature Genetics, a team of scientists from around the world analyzed the DNA sequences of 78,308 people for correlations with general intelligence, as measured by IQ tests.

The major goal of the study was to identify single nucleotide polymorphisms—or SNPs—that correlate significantly with intelligence test scores. Found in most cells throughout the body, DNA is made up of four molecules called nucleotides, referred to by their organic bases: cytosine (C), thymine (T), adenine (A), and guanine (G). Within a cell, DNA is organized into structures called chromosomes­. Humans normally have 23 pairs of chromosomes, with one in each pair inherited from each parent.

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