In humans, sex determination is the process that determines the biological sex of an offspring and, as a result, the sexual characteristics that they will develop. Humans typically develop as either male or female, primarily depending on the combination of sex chromosomes that they inherit from their parents. The human sex chromosomes, called X and Y, are structures in human cells made up of tightly bound deoxyribonucleic acid, or DNA, and proteins. Those are molecules that contain the instructions for the development and functioning of all life forms, including the development of physical traits and body parts that correspond with each biological sex. Humans who inherit two X chromosomes typically develop as females, while humans with one X and one Y chromosome typically develop as males. Sex determination is the beginning of the development of many characteristics that influence how a human looks and functions as well as the societal expectations that other humans have for each other.

John Langdon Down studied medicine in England in the nineteenth century and was one of the first people to develop a complete description of the disorder that would later be known as Trisomy 21, or Down Syndrome. Down Syndrome is a condition caused by the presence of an extra chromosome, which may cause a person to be born with certain impaired learning abilities and physical features such as a short neck, flattened face, and almond-shaped eyes. In 1866, Down published one of the first accounts to accurately describe people with Down Syndrome, or what he called “Mongolism,” and identify it as a distinct condition. Additionally, Down advocated for people with mental disabilities at a time when their families commonly abandoned them and medical professionals did not prioritize them. He improved the quality of care for people in the centers he worked in and increased their educational opportunities so they would be better prepared to live a normal life. Down brought increased attention to Down Syndrome, leading to the future discovery of the chromosomal anomaly that causes the disorder, and promoting a higher standard of care for people with mental disabilities.

As of 2022, Trisomy 21 is the most common type of trisomy, or a condition where the person has three instead of the normal two copies of one of the chromosomes. Trisomy occurs when abnormal cell division takes place leading to an extra copy of a chromosome. That extra copy of chromosome 21 results in a congenital disorder called Down syndrome, which is characterized by a cluster of specific traits including intellectual disabilities, atypical facial appearance, and a high risk of heart disease. Trisomy 21 changes the way in which a fetus’s brain develops, which accounts for many intellectual disabilities. The United States Centers for Disease Control and Prevention, or CDC, estimates Trisomy 21 occurs approximately once in every 700 human births, averaging about 6,000 live Down syndrome births every year in the US. Down syndrome is a lifelong developmental condition, but there are many resources available to those living with Down syndrome and their families.

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.

In 1975, the United States Congress passed the Individuals with Disabilities Education Act, referred to as the IDEA, which codified the right of all American children to a free and appropriate public education regardless of disability status. The IDEA requires all public schools that accept federal funds to provide education that meets the needs of students with disabilities at the public expense. Prior to IDEA, many students with disabilities went without any educational opportunities, and many faced confinement in institutions. The IDEA enshrined the right to education for children with disabilities, allowing millions of children to learn in a public-school classroom by setting guidelines for accessibility and the instruction of students with disabilities in American public schools.