In 2007, Françoise Baylis and Jason Scott Robert published “Part-Human Chimeras: Worrying the Facts, Probing the Ethics” in The American Journal of Bioethics. Within their article, hereafter “Part-Human Chimeras,” the authors offer corrections on “Thinking About the Human Neuron Mouse,” a report published in The American Journal of Bioethics in 2007 by Henry Greely, Mildred K. Cho, Linda F. Hogle, and Debra M. Satz, which discussed the debate on the ethics of creating part-human chimeras. Chimeras are organisms that contain two or more genetically distinct cell lines. Both publications discuss chimeras with DNA from different species, specifically in response to studies in which scientists injected human brain cells into mice. “Part-Human Chimeras,” contributes to a chain of ethical and scientific discussion that occurred in the mid-2000s on whether people should be able to conduct research on chimeras, especially in embryos.

In 2006, bioethicist Jason Scott Robert published “The Science and Ethics of Making Part-Human Animals in Stem Cell Biology” in The FASEB Journal. There, he reviews the scientific and ethical justifications and restrictions on creating part-human animals. Robert describes part-human animals, otherwise known as chimeras, as those resulting from the intentional combination of human and nonhuman cells, tissues, or organs at any stage of development. He specifically criticizes restrictions against creating part-human animals made by the National Academy of Sciences, or NAS, in 2005, arguing that while they ensure that such research is morally justifiable, they might limit scientists from conducting useful science using part-human animals or entities. Robert challenges the moral rationales behind prohibiting chimera research, arguing that they may impede scientists from conducting research that could have important benefits to biology and medicine, and suggests how to balance the conflicting moral and scientific needs of such science.

Breast augmentation involves the use of implants or fat tissue to increase patient breast size. As of 2019, breast augmentation is the most popular surgical cosmetic procedure in the United States, with annual patient numbers increasing by 41 percent since the year 2000. Since the first documented breast augmentation by surgeon Vincenz Czerny in 1895, and later the invention of the silicone breast implant in 1963, surgeons have developed the procedure into its own specialized field of surgery, creating various operating techniques for different results. By having varied incisions, implant placements, and improved ways of treating surgery-related complications, advanced technology has enabled women to undergo breast augmentations for aesthetic, medical, or reconstructive reasons. Trans women may also benefit from breast augmentations. Having the option of a breast augmentation gives women more control over their physical appearance, which may improve their self-image and boost their confidence.

In the 1960s, two plastic surgeons from the United States, Thomas Dillon Cronin and Frank Judson Gerow, collaborated with the Dow Corning Corporation, which specialized in silicone products, to create the first silicone breast implant. Surgeons used the implant, named the Cronin-Gerow implant, to improve the look of a woman’s breasts, by correcting for asymmetry, augmenting the size, or creating a more uplifted profile. Surgeons began widely using the breast implant almost immediately after it reached the US market in 1964, and breast augmentation quickly became one of the most popular cosmetic surgeries in the country. The creation of a silicone breast implant not only established a new branch of cosmetic surgery, but it also enabled women with breast cancer to receive reconstructions to improve their aesthetic appearance after cancer treatment and removal of the cancerous breast tissues.

In May 1953, scientists James Watson and Francis Crick wrote the article “Genetical Implications of the Structure of Deoxyribonucleic Acid,” hereafter “Genetical Implications,” which was published in the journal Nature. In “Genetical Implications,” Watson and Crick suggest a possible explanation for deoxyribonucleic acid, or DNA, replication based on a structure of DNA they proposed prior to writing “Genetical Implications.” Watson and Crick proposed their theory about DNA replication at a time when scientists had recently reached the consensus that DNA contained genes, which scientists understood to carry information that determines an organism’s identity. Watson and Crick’s replication mechanism as presented in “Genetical Implications” contributed to the two scientists sharing a portion of the 1962 Nobel Prize in Physiology or Medicine. With their suggested DNA replication mechanism in “Genetical Implications,” Watson and Crick explained how genes are copied and passed along to new cells and organisms, thereby explaining how the information contained within genes is preserved through generations.

Walter Jakob Gehring discovered the homeobox, a DNA segment found in a specific cluster of genes that determine the body plan of animals, plants, and fungi. Gehring identified the homeobox in 1983, with the help of colleagues while isolating the Antennapedia (Antp) gene in fruit flies (Drosophila) at the University of Basel in Basel, Switzerland. Hox genes, a family of genes that have the homeobox, determine the head-to-tail (anterior-posterior) body axis of both vertebrates and invertebrates. Gehring also identified the homeobox-containing Pax-6 gene as the master control gene in eye development of Drosophila, the same gene that, when mutated or absent in humans, leads to aniridia, or lack of the iris, in humans. Gehring's work with the homeobox suggested to biologists that widely different species share a similar and evolutionarily conserved genetic pathway that controls the development of overall body plans, from fruit flies to humans.

During the twentieth century in the United States, Alfred Day Hershey studied phages, or viruses that infect bacteria, and experimentally verified that genes were made of deoxyribonucleic acid, or DNA. Genes are molecular, heritable instructions for how an organism develops. When Hershey started to study phages, scientists did not know if phages contained genes, or whether genes were made of DNA or protein. In 1952, Hershey and his research assistant, Martha Chase, conducted phage experiments that convinced scientists that genes were made of DNA. For his work with phages, Hershey shared the 1969 Nobel Prize in Physiology or Medicine with Max Delbrück and Salvador Luria. Hershey conducted experiments with results that connected DNA to the function of genes, thereby changing the way scientists studied molecular biology and the development of organisms.

Between 1957 and 1959, Arthur Pardee, Francois Jacob, and Jacques Monod conducted a set of experiments at the Pasteur Institute in Paris, France, that was later called the PaJaMa Experiments, a moniker derived from the researchers' last names. In these experiments, they described how genes of a species of single-celled bacteria, called Escherichia coli (E. coli), controlled the processes by which enzymes were produced in those bacteria. In 1959, the researchers published their results in a paper titled 'The Genetic Control and Cytoplasmic Expression of 'Inducibility' in the Synthesis of b-galactosidase by E. coli'. When they compared mutated strains of E. coli to a normal strain, Pardee, Jacob, and Monod identified the abnormal regulation processes and enzymes produced by the mutated genes. The results showed how enzymes break down the molecules that the bacteria ingested. The PaJaMas experiments uncovered some of the molecular mechanisms that regulate how some genes yield enzymes in many species.

Multiplex Automated Genome Engineering, or MAGE, is a genome editing technique that enables scientists to quickly edit an organism’s DNA to produce multiple changes across the genome. In 2009, two genetic researchers at the Wyss Institute at Harvard Medical School in Boston, Massachusetts, Harris Wang and George Church, developed the technology during a time when researchers could only edit one site in an organism’s genome at a time. Wang and Church called MAGE a form of accelerated evolution because it creates different cells with many variations of the same original genome over multiple generations. MAGE made genome editing much faster, cheaper, and easier for genetic researchers to create organisms with novel functions that they can use for a variety of purposes, such as making chemicals and medicine, developing biofuels, or further studying and understanding the genes that can cause harmful mutations in humans.

The Y-chromosome is one of a pair of chromosomes that determine the genetic sex of individuals in mammals, some insects, and some plants. In the nineteenth and twentieth centuries, the development of new microscopic and molecular techniques, including DNA sequencing, enabled scientists to confirm the hypothesis that chromosomes determine the sex of developing organisms. In an adult organism, the genes on the Y-chromosome help produce the male gamete, the sperm cell. Beginning in the 1980s, many studies of human populations used the Y-chromosome gene sequences to trace paternal lineages. In mammals, the Y-chromosomes contain the master-switch gene for sex determination, called the sex-determining region Y, or the SRY gene in humans. In most normal cases, if a fertilized egg cell, called a zygote, has the SRY gene, the zygote develops into an embryos that has male sex traits. If the zygote lacks the SRY gene or if the SRY gene is defective, the zygote develops into an embryo that has female sex traits.