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Sex-determining Region Y in Mammals

The Sex-determining Region Y (Sry in mammals but SRY in humans) is a gene found on Y chromosomes that leads to the development of male phenotypes, such as testes. The Sry gene, located on the short branch of the Y chromosome, initiates male embryonic development in the XY sex determination system. The Sry gene follows the central dogma of molecular biology; the DNA encoding the gene is transcribed into messenger RNA, which then produces a single Sry protein.

Format: Articles

Subject: Processes

Leuprorelin as a Treatment for Endometriosis

Leuprolide acetate, or leuprorelin, is a manufactured drug that has been prescribed as a treatment for endometriosis, a medical condition in which body tissue that typically lines the uterus grows outside of the uterus, since 1989. Leuprorelin is a modified version of a gonadotropin-releasing hormone, a type of hormone that helps regulate the female menstrual cycle. The drug inhibits the production of estrogen, a female sex hormone that enables endometrial gland growth.

Format: Articles

Subject: Processes

Multi-Fetal Pregnancy

In humans, multi-fetal pregnancy occurs when a mother carries more than one fetus during the pregnancy. The most common multi-fetal pregnancy is twins, but mothers have given birth to up to eight children (octuplets) from a single pregnancy. Multiple fetusus can result from the release of multiple eggs or multiple ovulations, the splitting of a single fertilized egg, and fertility treatments such as in vitro fertilization (IVF) which involves the insertion of many fertilized eggs into the mother's uterus.

Format: Articles

Subject: Processes, Reproduction

Post-Coital Oral Emergency Contraception

Post-coital oral emergency contraception is used for the prevention of pregnancy after intercourse. The contraception comes in the form of pills, often collectively referred to as morning-after pills. Post-coital use of morning-after pills separates them from traditional contraception which is either a continual preventative process, such as the birth control pill, or used during intercourse, such as condoms.

Format: Articles

Subject: Processes, Reproduction

Meiosis in Humans

Meiosis, the process by which sexually-reproducing organisms generate gametes (sex cells), is an essential precondition for the normal formation of the embryo. As sexually reproducing, diploid, multicellular eukaryotes, humans rely on meiosis to serve a number of important functions, including the promotion of genetic diversity and the creation of proper conditions for reproductive success.

Format: Articles

Subject: Processes, Reproduction

Intraspecies Chimeras Produced in Laboratory Settings (1960-1975)

When cells-but not DNA-from two or more genetically distinct individuals combine to form a new individual, the result is called a chimera. Though chimeras occasionally occur in nature, scientists have produced chimeras in a laboratory setting since the 1960s. During the creation of a chimera, the DNA molecules do not exchange genetic material (recombine), unlike in sexual reproduction or in hybrid organisms, which result from genetic material exchanged between two different species. A chimera instead contains discrete cell populations with two unique sets of parental genes.

Format: Articles

Subject: Organisms, Processes

Amniocentesis Prior to 1980

The extraembryonic membranes that surround and originate from the embryos of vertebrates such as birds, reptiles, and mammals are crucial to their development. They are integral to increasing the surface area of the uterus, forming the chorion (which in turn produces the placenta) and the amnion, respectively. The amnion will ultimately surround the embryo in a fluid-filled amniotic cavity. This amniotic fluid, which cushions and protects the fetus and helps prevent the onset of labor, is sampled in amniocentesis to screen for genetic diseases.

Format: Articles

Subject: Processes, Reproduction

Circulatory Changes at Birth

When placental mammals are born their circulatory systems undergo radical changes as the newborns are prepared for independent life. The lungs are engaged, becoming the primary source of fresh oxygen, replacing the placental barrier as a means for blood-gas exchange.

Format: Articles

Subject: Processes

Chemical Induction

Research in chemical induction seeks to identify the compound or compounds responsible for differentiation in a developing embryo. Soren Lovtrup compared the search for these compounds to the search for the philosopher's stone. It was based on the assumption that the differentiating agents have to be chemical substances either within cells or in the extracellular matrix.

Format: Articles

Subject: Processes

Hartsoeker's Homunculus Sketch from Essai de Dioptrique

This embryology image is a pencil sketch by Nicolaas Hartsoeker, published as part of his 1694 French-language paper entitled Essai de Dioptrique, a semi-speculative work describing the sorts of new scientific observations that could be done using magnifying lenses. Dioptrique was published in Paris by the publishing house of Jean Anisson. The image depicts a curled up infant-like human, now referred to as a homunculus, inside the head of a sperm cell.

Format: Articles

Subject: Theories, Processes

Epithelium

Frederik Ruysch, working in the Netherlands, introduced the term epithelia in the third volume of his Thesaurus Anatomicus in 1703. Ruysch created the term from the Greek epi, which means on top of, and thele, which means nipple, to describe the type of tissue he found when dissecting the lip of a cadaver. In the mid nineteenth century, anatomist Albrecht von Haller adopted the word epithelium, designating Ruysch's original terminology as the plural version. In modern science, epithelium is a type of animal tissue in which cells are packed into neatly arranged sheets.

Format: Articles

Subject: Theories, Processes

Abortion

Abortion is the removal of the embryo or fetus from the womb, before birth can occur-either naturally or by induced labor. Prenatal development occurs in three stages: the zygote, or fertilized egg; the embryo, from post-conception to eight weeks; and the fetus, from eight weeks after conception until the baby is born. After abortion, the infant does not and cannot live. Spontaneous abortion is the loss of the infant naturally or accidentally, without the will of the mother. It is more commonly referred to as miscarriage.

Format: Articles

Subject: Processes, Ethics, Reproduction

Biological Clocks and the Formation of Human Tooth Enamel

Tooth enamel contains relics of its formation process, in the form of microstructures, which indicate the incremental way in which it forms. These microstructures, called cross-striations and striae of Retzius, develop as enamel-forming cells called ameloblasts, whcih cyclically deposit enamel on developing teeth in accordance with two different biological clocks. Cross-striations result from a twenty-four hour cycle, called a Circadian rhythm, in the enamel deposition process, while striae of Retzius have a longer periodicity.

Format: Articles

Subject: Processes

Inducing Fertilization and Development in Sand Dollars

Sand dollars are common marine invertebrates in the phylum Echinodermata and share the same class (Echinoidea) as sea urchins. They have served as model laboratory organisms for such embryologists as Frank Rattray Lillie and Ernest Everett Just. Both Lillie and Just used Echinarachnius parma for their studies of egg cell membranes and embryo development at the Marine Biological Laboratory (MBL) at Woods Hole, Massachusetts, in the early 1900s.

Format: Articles

Subject: Processes

Process of Eukaryotic Embryonic Development

All sexually reproducing, multicellular diploid eukaryotes begin life as embryos. Understanding the stages of embryonic development is vital to explaining how eukaryotes form and how they are related on the tree of life. This understanding can also help answer questions related to morphology, ethics, medicine, and other pertinent fields of study. In particular, the field of comparative embryology is concerned with documenting the stages of ontogeny.

Format: Articles

Subject: Processes