In re Marriage of Witten, decided by the Iowa Supreme Court in 2003, held that neither Tamera nor Arthur (Trip) Witten could use or destroy several cryopreserved preembryos created during their marriage using in vitro fertilization (IVF), unless the former couple could reach a mutual agreement. Tamera and Trip Witten, unable to conceive conventionally during their marriage, had attempted to start a family together using IVF at the University of Nebraska Medical Center (UNMC) in Omaha, Nebraska. When Trip sought to dissolve the marriage in April 2002, following several unsuccessful IVF attempts, seventeen of their preembryos were in storage at UNMC. The former couple disagreed about what should happen to the preembryos and asked the court for a resolution as part of the marital dissolution action. The high court of Iowa’s decision to restrict both individuals from using the cryopreserved preembryos without the other person’s consent reflected a belief that Tamera and Trip shared equal decision-making authority over the preembryos.

Ectoderm is one of three germ layers--groups of cells that coalesce early during the embryonic life of all animals except maybe sponges, and from which organs and tissues form. As an embryo develops, a single fertilized cell progresses through multiple rounds of cell division. Eventually, the clump of cells goes through a stage called gastrulation, during which the embryo reorganizes itself into the three germ layers: endoderm, ectoderm, and mesoderm. After gastrulation, the embryo goes through a process called neurulation, which starts the development of nervous system.

Possums is a 174-page book consisting of a series of essays written about the Virginia opossum (Didelphis virginiana), the only living marsupial in the US. The essays were written by Carl Gottfried Hartman, an embryologist at the Carnegie Institute of Washington (CIW), in Baltimore, Maryland, who also worked with another mammal, the rhesus monkey. Possums was published in 1952 by Hartman's alma mater, the University of Texas at Austin (UT). Beginning in 1913, while as a graduate student, and later as an instructor at UT, Hartman captured and raised opossums. He was one of the first zoologists to study the intricacies of opossum embryology, leading to an account of the embryology and reproductive physiology of a mammal from the wild, rather than of a mammal bred exclusively for laboratory research. Possums culminated Hartman's studies of the marsupial.

In the late 1980s, Peter Goodfellow in London, UK led a team of researchers who showed that the SRY gene in humans codes a protein that causes testes to develop in embryos. During this time, scientists in London and Paris, including Peter Koompan and John Gubbay, proposed that SRY was the gene on the Y chromosome responsible for encoding the testis-determining factor (TDF) protein. The TDF is a protein that initiates embryo to develop male characteristics. Looking for evidence that SRY was the TDF, Goodfellow and colleagues examined people who were anatomically female, but whose cells had Y chromosomes. Females normally have cells with two X sex chromosomes (XX), while males normally have cells with one X and one Y chromosome (XY). Goodfellow's team discovered that individuals with Y chromosomes developed as female instead of as male due to inactive SRY sequences on the Y chromosome. Goodfellow and colleagues compiled the results of their experiment in a paper titled Genetic Evidence Equating SRY and the Testis-Determining Factor in 1990. Their results showed that the SRY gene is necessary for male characteristics to develop in embryos, and that SRY encodes the TDF protein.

Congenital rubella syndrome (CRS) can occur in children whose mothers contracted the rubella virus, sometimes called German measles, during pregnancy. Depending on the gestational period when the mother contracts rubella, an infant born with CRS may be unaffected by the virus or it may have severe developmental defects. The most severe effects of the virus on fetal development occur when the mother contracts rubella between conception and the first trimester. Defects from maternal rubella in the first trimester are included in the term congenital rubella syndrome, but physicians and researchers specifically refer to those defects as rubella embryopathy. Developmental defects are less severe if the mother contracts rubella in the second trimester, and they are generally negligible if the infection occurs in the third trimester. Prenatal rubella infection can cause birth defects which include deafness, compromised vision, abnormal heart development, and damage to the central nervous system which can lead to compromised cognition and learning disabilities.

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.

The South Korean government passed the Bioethics and Biosafety Act, known henceforth as the Bioethics Act, in 2003 and it took effect in 2005. South Korea's Ministry of Health and Welfare proposed the law to the South Korean National Assembly to allow the progress of biotechnology and life sciences research in South Korea while protecting human research subjects with practices such as informed consent. The Bioethics Act establishes a National Bioethics Committee in Seoul, South Korea. The Bioethics Act is the first law in South Korea to regulate research on embryonic stem cells and in vitro fertilization. Most South Korean bioethical policies rely on this act and its provisions.

Implantation is a process in which a developing embryo, moving as a blastocyst through a uterus, makes contact with the uterine wall and remains attached to it until birth. The lining of the uterus (endometrium) prepares for the developing blastocyst to attach to it via many internal changes. Without these changes implantation will not occur, and the embryo sloughs off during menstruation. Such implantation is unique to mammals, but not all mammals exhibit it. Furthermore, of those mammals that exhibit implantation, the process differs in many respects between those mammals in which the females have estrous cycles, and those mammals in which the femals have menstrual cycles. Females in the different species of primates, including humans, have menstrual cycles, and thus similar processes of implantation.

To study human evolution, researchers sometimes use microstructures found in human teeth and their knowledge of the processes by which those structures grow. Human fetusus begin to develop teeth in utero. As teeth grow, they form a hard outer substance, called enamel, through a process called amelogenesis. During amelogenesis, incremental layers of enamel form in a Circadian rhythm. This rhythmic deposition leaves the enamel with microstructures, called cross-striations and striae of Retzius, which have a regular periodicity. Because enamel is not renewed throughout life like other tissues, teeth preserve the timing and details of a person's growth and development. Thus, enamel microstructures, from living people and from fossilized teeth, can be used to reconstruct the growth, development, and life histories of current and past humans. Researchers can also compare current and fossilized microstructures to trace changes in those traits over the course of human evolution.

The Notch signaling pathway is a mechanism in animals by which adjacent cells communicate with each other, conveying spatial information and genetic instructions for the animal's development. All multicellular animals utilize Notch signaling, which contributes to the formation, growth, and development of embryos (embryogenesis). Notch signaling also contributes to the differentiation of embryonic cells into various types of cells into various types of cells, such as neurons. Research into the Notch gene in fruit flies began in the early twentieth century, but not until the end of the twentieth century did researchers begin to uncover, in many different species, the roles of Notch proteins for cell to cell signaling. Researchers have also found that dysfunction in the pathway can contribute to diseases such as cancer and Alzheimer's.