Julia Bell worked in twentieth-century Britain, discovered Fragile X Syndrome, and helped find heritable elements of other developmental and genetic disorders. Bell also wrote much of the five volume Treasury of Human Inheritance, a collection about genetics and genetic disorders. Bell researched until late in life, authoring an original research article on the effects of the rubella virus of fetal development (Congenital Rubella Syndrome) at the age of 80.

Mitochondrial DNA (mtDNA) is located outside the nucleus in the liquid portion of the cell (cytoplasm) inside cellular organelles called Mitochondria. Mitochondria are located in all complex or eukaryotic cells, including plant, animal, fungi, and single celled protists, which contain their own mtDNA genome. In animals with a backbone, or vertebrates, mtDNA is a double stranded, circular molecule that forms a circular genome, which ranges in size from sixteen to eighteen kilo-base pairs, depending on species. Each mitochondrion in a cell can have multiple copies of the mtDNA genome. In humans, the mature egg cell, or oocyte, contains the highest number of mitochondria among human cells, ranging from 100,000 to 600,000 mitochondria per cell, but each mitochondrion contains only one copy of mtDNA. In human embryonic development, the number of mitochondria, the content of mtDNA in each mitochondrion, and the subsequent mtDNA activity affects the production of the oocytes, fertilization of the oocytes, and early embryonic growth and development.

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.

In a series of experiments in the late 1970s, Alec J. Jeffreys in the UK and Richard A. Flavell in the Netherlands developed a technique to detect variations in the DNA of different individuals. They compared fragments of DNA from individuals’ beta-globin genes, which produce a protein in hemoglobin. Previously, to identify biological material, scientists focused on proteins rather than on genes. But evidence about proteins enabled scientists only to exclude, but not to identify, individuals as the sources of the biological samples. By 1979, Jeffrey’s experiments on beta-globin genes shifted the analytical approach of scientific identification from proteins to genes to identify an individual’s genetic identity. The ability to match a person to a biological sample developed in the 1980s and impacted many fields including paternity testing, forensics, immigration, and body identification.

National Geographic's documentary In the Womb: Identical Twins focuses on the prenatal development of human identical twins. Director Lorne Townend uses three-dimensional (3D) and four-dimensional (4D) ultrasound imaging and microscopy to depict twin development , genetic and epigenetic variations in the fetuses, and methods of fetal survival in the confines of the womb. Artist renditions of scientific data fill in areas of development inaccessible to the imaging tools. The 50-minute film describes the lives twins live after birth and describes new research that identical twins might not be as identical as once thought. In the womb: Identical Twins is a sequel to the 2005 National Geographic film In the Womb.

In 1959, Charles Edmund Ford and colleagues published “A Sex Chromosome Anomaly in a Case of Gonadal Dysgenesis (Turner’s Syndrome),” hereafter “A Sex Chromosome Anomaly,” in The Lancet. Turner syndrome is a chromosomal disorder that affects one in 2,000 female births and results in developmental issues such as short stature, infertility, and congenital heart disease. Prior to “A Sex Chromosome Anomaly,” researchers did not know the cause of Turner syndrome, but Ford and colleagues found that the cause is a sex chromosome irregularity. In the article, the team explains that they examined the cells of a person with Turner syndrome and determined that she had just one X chromosome instead of the typical two. Thus, they concluded that the cause of Turner syndrome is a missing X chromosome and called for a new classification of the condition. “A Sex Chromosome Anomaly” was one of the first papers to identify the cause of Turner syndrome, and it provided scientists with a better understanding of individuals with a nontypical sex chromosome pattern.