In 1938, physician Henry Hubert Turner published “A Syndrome of Infantilism, Congenital Webbed Neck, and Cubitus Valgus,” hereafter “A Syndrome of Infantilism,” in the journal Endocrinology, in which he described a condition that researchers later named Turner syndrome. Turner syndrome is a genetic condition that affects biological females, characterized by a partially or completely missing X chromosome. In the paper, Turner describes a previously unrecognized set of symptoms in seven different females, including a lack of physical and sexual development, infertility, webbed neck, and elbow deformities, among others. Turner also records various methods of hormone treatments for his patients, such as growth hormone and estrogen injections. “A Syndrome of Infantilism” was one of the first published descriptions of Turner syndrome, a developmental condition that affects one in 2,500 live female births globally, and highlighted the use of hormone treatments to promote the development of stunted physical and sexual growth.

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.

In 1961, Mary Lyon, a researcher who studied genetics, published “Gene Action in the X-chromosome of the Mouse (Mus Musculus L.),” hereafter “Gene Action in the X-chromosome,” in the journal Nature. Lyon’s paper focuses on the workings of female sex chromosomes, or X-chromosomes, and their implications for gene expression. A chromosome is a structure in a cell’s nucleus that contains the DNA, or genetic information, for each individual. In her paper, Lyon proposes her X-inactivation hypothesis, which states that one of the two X-chromosomes in mammalian female cells becomes inactive during early development, silencing its genetic activity. By describing X-chromosome inactivation, Lyon provided an explanation for the mosaic patterns observed in some female mammals, where different regions of their bodies exhibit distinct traits based on the genes carried by the particular X-chromosome that is active in that region. “Gene Action in the X-chromosome” provided evidence that X-chromosome inactivation occurs, laying the basis for understanding sex-linked traits, gene expression, and X-linked genetic diseases that impact thousands of people.