The Origin and Behavior of Mutable Loci in Maize, by Barbara McClintock, was published in 1950 in the Proceedings of the National Academy of Sciences of the United States of America. McClintock worked at the Cold Spring Harbor Laboratory in Laurel Hollow, New York, at the time of the publication, and describes her discovery of transposable elements in the genome of corn (Zea mays). Transposable elements, sometimes called transposons or jumping genes, are pieces of the chromosome capable of physically changing positions along the chromosome. The Origin and Behavior explains the mechanics of development that occur in maize kernels, which are plant embryos.

Isotretinoin is a molecule and a byproduct (metabolite) of vitamin A, and in greater than normal amounts in pregnant women, it can cause fetal abnormalities including cleft lips, ear and eye defects, and mental retardation. Isotretinoin is commonly called by its trade name Accutane, and it's a chemical compound derived from vitamin A, or retinoic acid. Doctors prescribe isotretinoin to treat severe acne. For pregnant women, too much vitamin A or isotretinoin can also cause greater than normal rates of stillbirths and fetal disintegrations after the ninth week of gestation. Women who use isotretinoin during the first trimester of their pregnancies, even in small amounts, risk defects to their fetuses such as external ear malformations, cleft palates, undersized jaws (micrognathia), a variety of heart defects, buildups of fluids inside the skulls that leads to brain swelling (hydrocephalus), small heads and brains (microcephaly), and mental retardation.