At the turn of the twentieth century, William Bateson studied organismal variation and heredity of traits within the framework of evolutionary theory in England. Bateson applied Gregor Mendel's work to Charles Darwin's theory of evolution and coined the term genetics for a new biological discipline. By studying variation and advocating Mendelian genetics, Bateson furthered the field of genetics, encouraged the use of experimental methodology to study heredity, and contributed to later theories of genetic inheritance.

Susumu Ohno studied chromosome structure and evolution during the twentieth century in the United States. Ohno was one of the first researchers to propose that the Barr body, a mass of genetic material within female mammalian cells, was a condensed X-chromosome. Ohno also developed a theory that gene duplication, when specific regions of a chromosome become multiplied, is a primary driver of evolution, with natural selection playing a secondary role. He theorized that gene duplication allows one copy of the original gene to remain and perform its normal function while a second copy of the gene can mutate and undergo natural selection, leading to diversification of life. Later in his career, Ohno composed music based on DNA sequences. As of 2025, researchers continue to debate Ohno’s theory of gene duplication. Through his research, Ohno introduced a new perspective on the driving forces of evolution, which advanced researchers’ understanding of chromosomal evolution and genetic diversity.

Luigi Luca Cavalli-Sforza (1922–2018) was a researcher whose work explored the relationships between human genetic diversity and historical migrations, integrating genetics and anthropology to determine how humans populated the world. Prior to his work in human genetics, Cavalli-Sforza studied genetic recombination in bacteria and helped determine the system of genetic inheritance within Escherichia coli in the late 1940s. After pivoting his research focus and assuming a long-term teaching and research position at Stanford University in Stanford, California, in 1971, Cavalli-Sforza participated in studies that modeled human migration, focusing on the global spread of agriculture during the Neolithic period. He was also one of the founders in the creation of the Human Genome Diversity Project, or HGDP, an international scientific collaboration launched in the early 1990s to map the genetic diversity of human populations across the globe. Cavalli-Sforza’s interdisciplinary approach to studying human history and human evolution left its mark on the fields of both genetics and anthropology in the twentieth and twenty-first centuries.

Launched in 2002, the International HapMap Project was a collaborative effort among scientists from around the world to create a map of common patterns of genetic variation in the human genome. HapMap stands for haplotype map. A haplotype is a stretch of DNA nucleotides, or letters, that individuals inherit as a block because they lie relatively close together along a chromosome. For any particular region of a chromosome, there may be multiple different haplotypes present among humans, each characterized by a slightly different DNA sequence. By collecting and sequencing the DNA of initially 270 individuals from several different geographic regions, HapMap scientists were able to identify common haplotypes that exist among those individuals, as well as reliable markers to distinguish them. That collection of haplotypes and identifying markers—the HapMap—provided a shortcut for researchers who wanted to identify associations between those inherited DNA variants and particular human traits, especially common, complex diseases like heart disease and cancer.