When cells-but not DNA-from two or more genetically distinct individuals combine to form a new individual, the result is called a chimera. Though chimeras occasionally occur in nature, scientists have produced chimeras in a laboratory setting since the 1960s. During the creation of a chimera, the DNA molecules do not exchange genetic material (recombine), unlike in sexual reproduction or in hybrid organisms, which result from genetic material exchanged between two different species. A chimera instead contains discrete cell populations with two unique sets of parental genes. Chimeras can occur when two independent organisms fuse at a cellular level to form one organism, or when a population of cells is transferred from one organism to another. Chimeras created in laboratories have helped scientists to identify developmental mechanisms and processes across species. Some experiments involving chimeras aim to provide further knowledge of immune reactions against disease or to create animal models to understand human disease.
The National Association for Down Syndrome, or NADS, is an organization that was founded in 1960 by Kathryn McGee in Chicago, Illinois, to support people with Down syndrome and their families in improving their quality of life. Originally named the Mongoloid Developmental Council, NADS is one of the oldest organizations serving people with Down syndrome and their families in the United States. According to NADS, Down syndrome is a genetic condition that occurs in one in every seven hundred ninety-two people and that causes delays in physical and intellectual development. Members of NADS work to provide information, resources, and access to services and programs for families with Down syndrome, educate the public, address social policy issues and challenges, and facilitate advocacy efforts within the Down syndrome community. For over sixty years, NADS has helped support individuals born with Down syndrome, one of the most common genetic disorders, in the US to find acceptance, develop their capabilities, and work toward independence.
Henry Hubert Turner was a physician and researcher who studied hormones and human development in Oklahoma City, Oklahoma, during the twentieth century. He was one of the first people to classify Turner syndrome, which is a genetic condition that occurs when someone has a specific atypical chromosomal pattern, and as of 2024, affects one in 1,500 to 2,500 female births. Turner syndrome results in a biological female completely or partially missing one of their X chromosomes. Many researchers label it an intersex condition, or a condition in which someone has atypical male or female sex characteristics, such as different sex chromosome patterns. During his career, Turner encountered multiple patients with a specific set of symptoms, including stunted sexual development, webbed neck, and elbow deformities, and he was unable to place those symptoms under one existing diagnosis. So, he categorized those symptoms as a new syndrome, which researchers later named Turner syndrome. By identifying Turner syndrome as a developmental condition, Turner helped future physicians develop treatments and diagnostic tools that can improve the lives of individuals with various developmental disorders.