Embryo Project Encyclopedia

Frank Rattray Lillie's research on freemartins from 1914 to 1920 in the US led to the theory that hormones partly caused for sex differentiation in mammals. Although sometimes applied to sheep, goats, and pigs, the term freemartin most often refers to a sterile cow that has external female genitalia and internal male gonads and was born with a normal male twin. Lillie theorized that a freemartin is a genetic female whose process of sexual development from an undifferentiated zygote was suppressed or antagonized by her twin's release of male hormones via their shared blood circulation in utero. Despite publications of similar findings by physician Julius Tandler in Vienna, Austria, in 1910 and physician Karl Keller in Wiesensteig, Germany in 1916 prior to Lillie's research, Lillie often receives credit for the hormonal theory of sex differentiation in the freemartin. Lillie's study of freemartins, and the subsequent research by graduate students in Lillie's laboratory at the University of Chicago in Chicago, Illinois, prompted many embryologists to research sex differentiation and hermaphroditism in mammals.

Francis Harry Compton Crick, who co-discovered the structure of deoxyribonucleic acid (DNA) in 1953 in Cambridge, England, also developed The Central Dogma of Molecular Biology, and further clarified the relationship between nucleotides and protein synthesis. Crick received the Nobel Prize in Physiology or Medicine that he shared with James Watson and Maurice Wilkins in 1962 for their discovery of the molecular structure of DNA. Crick's results on the genetic material found in all living organisms advanced theories of inheritance and spurred further studies into the field of genetics and embryology.

Farmers have long relied on genetic diversity to breed new crops, but in the early 1900s scientists began to study the importance of plant genetic diversity for agriculture. Scientists realized that seed crops could be systematically bred with their wild relatives to incorporate specific genetic traits or to produce hybrids for more productive crop yields. The spread of hybrids led to less genetically diversity than normal plant populations, however, and by 1967, plant scientists led an international movement for conservation of plant genetic resources through the United Nations's Food and Agricultural Organization, and later through the Consultative Group for International Agricultural Research, both of which are headquartered in Europe. To conserve plant genetic resources, researchers must collect and store plant germplasm-the genetic material required to propagate a plant-usually in the form of a seed.

In 1947, Carl Richard Moore, a researcher at the University of Chicago, in Chicago, Illinois, wrote Embryonic Sex Differentiation and Sex Hormones, which was published in the same year as a first-edition monograph. In the book, Moore argues that regulation of sex differentiation in mammals is not controlled by sex hormones secreted by embryonic sex organs (gonads), but is controlled by non-hormonal genetic factors. In support of his hypothesis, Moore describes the current literature on sex differentiation, and he reviews experiments on vertebrates and invertebrates and his own work with opossum (Didelphis virginiana) young.

Hermaphrodites and the Medical Invention of Sex, by historian of science Alice Domurat Dreger, was published in 1998 by Harvard University Press. In the book, Dreger describes how many doctors and scientists treated human hermaphrodites from the late nineteenth century to the early twentieth century. She states that during this time period, many physicians and scientists struggled to determine the nature sex, and to support a classification of sex as male or female, many physicians and scientists resorted to viewing a person's gonads for identification of his or her sex. At the time that this book was published, Dreger was a faculty associate at the Center for Ethics and Humanities in the Life Sciences at the College of Medicine, University of Michigan, Michigan.

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.