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Temperature-Dependent Sex Determination in Reptiles

The sex of a reptile embryo partly results from the production of sex hormones during development, and one process to produce those hormones depends on the temperature of the embryo's environment. The production of sex hormones can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination, also called genetic or chromosomal sex determination, an organism's genes determine which hormones are produced.

Format: Articles

Subject: Experiments

Social Implications of Non-Invasive Blood Tests to Determine the Sex of Fetuses

By 2011, researchers in the US had established that non-invasive blood tests can accurately determine the gender of a human fetus as early as seven weeks after fertilization. Experts predicted that this ability may encourage the use of prenatal sex screening tests by women interested to know the gender of their fetuses. As more people begin to use non-invasive blood tests that accurately determine the sex of the fetus at 7 weeks, many ethical questions pertaining to regulation, the consequences of gender-imbalanced societies, and altered meanings of the parent-child relationship.

Format: Articles

Subject: Reproduction, Ethics, Legal

"The Adaptive Significance of Temperature-Dependent Sex Determination in a Reptile" (2008), by Daniel Warner and Richard Shine

In 2008 researchers Daniel Warner and Richard Shine tested the Charnov-Bull model by conducting experiments on the Jacky dragon (Amphibolurus muricatus), in Australia. Their results showed that temperature-dependent sex determination(TSD) evolved in this species as an adaptation to fluctuating environmental temperatures. The Charnov-Bull model, proposed by Eric Charnov and James Bull in 1977, described the evolution of TSD, although the model was, for many years, untested.

Format: Articles

Subject: Experiments

Beadle and Ephrussi Show that Something Besides Eye Tissue Determines Eye Color in Fruit Flies

Object is a digital image of fruit flies, and it has three panes. The first pane shows two fruit fly larvae, with one having its optic disc removed and the other getting that disc inserted in its abdomen. The second pane shows an adult fruit fly, a donee, which has a normal colored eye in its abdomen. The third pane shows an adult fruit fly, a donee, which has an abnormally colored eye in its abdomen.

In the 1930s, George Beadle and Boris Ephrussi discovered factors that affect eye colors in developing fruit flies. They did so while working at the California Institute of Technology in Pasadena, California. (1) They took optic discs (colored fuchsia in the image) from fruit fly larvae in the third instar stage of development. Had the flies not been manipulated, they would have developed into adults with vermilion eyes.

Format: Graphics

Subject: Experiments, Organisms

Studies in Spermatogenesis (1905), by Nettie Maria Stevens

Studies in Spermatogenesis is a two volume book written by Nettie Maria Stevens, and published by the Carnegie Institution of Washington in 1905 and 1906. In the books Stevens explains the research she conducted on chromosomal sex determination in the sperm and egg cells of insect species while at Bryn Mawr College, near Philadelphia, Pennsylvania. Studies in Spermatogenesis described early examples of chromosomal XY sex-determination.

Format: Articles

Subject: Publications

"Genetic Evidence Equating SRY and the Testis-Determining Factor" (1990), by Phillippe Berta et al.

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.

Format: Articles

Subject: Experiments

"Male Development of Chromosomally Female Mice Transgenic for Sry gene" (1991), by Peter Koopman, et al.

Early 1990s research conducted by Peter Koopman, John Gubbay, Nigel Vivian, Peter Goodfellow, and Robin Lovell-Badge, showed that chromosomally female (XX) mice embryos can develop as male with the addition of a genetic fragment from the Y chromosome of male mice. The genetic fragment contained a segment of the mouse Sry gene, which is analogous to the human SRY gene. The researchers sought to identify Sry gene as the gene that produced the testis determining factor protein (Tdf protein in mice or TDF protein in humans), which initiates the formation of testis.

Format: Articles

Subject: Experiments

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

The Discovery of The Dikika Baby Fossil as Evidence for Australopithecine Growth and Development

When scientists discovered a 3.3
million-year-old skeleton of a child of the human lineage (hominin) in
2000, in the village of Hadar, Ethiopia, they were able to study growth
and development of Australopithecus
afarensis, an extinct hominin species. The team of researchers,
led by Zeresenay Alemseged of the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany, named the fossil DIK 1-1 and nicknamed
it Dikika baby after the Dikika research site. The Dikika fossil

Format: Articles

Subject: Theories

The Y-Chromosome in Animals

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.

Format: Articles

Subject: Reproduction, Theories

Theophilus Shickel Painter (1889-1969)

Theophilus Shickel Painter studied the structure and
function of chromosomes in the US during in the early to mid-twentieth century. Painter worked at
the University of Texas at Austin in Austin, Texas. In the 1920s
and 1930s, Painter studied the chromosomes of the salivary gland
giant chromosomes of the fruit fly (Drosophila
melanogaster), with Hermann J. Muller. Muller and Painter
studied the ability of X-rays to cause changes in the chromosomes
of fruit flies. Painter also studied chromosomes in mammals.

Format: Articles

Subject: People

“A Linkage Between DNA Markers on the X Chromosome and Male Sexual Orientation” (1993), by Dean H. Hamer and Charles A. Thomas.

In 1993, Dean H. Hamer and colleagues in the US published results from their research that indicated that men with speicifc genes were more likely to be homosexual than were men without those genes. The study hypothesized that some X chromosomes contain a gene, Xq28, that increases the likelihood of an individual to be homosexual. Prior to those results, researchers had argued that the cause of homosexuality was environmental and that homosexuality could be altered or reversed. Hamer’s research suggested a possible genetic cause of homosexuality.

Format: Articles

Subject: Experiments

Nettie Maria Stevens (1861-1912)

Multiple theories about what determines sex were tested at the turn of the twentieth century. By experimenting on germ cells, cytologist Nettie Maria Stevens collected evidence to support the connection between heredity and the sex of offspring. Stevens was able to interpret her data to conclude that chromosomes have a role in sex determination during development. For her time, she was an emerging breed: a woman of science making the leap from the world of data collection to that of male-dominated interpretive work.

Format: Articles

Subject: People, Reproduction

The Apgar Score (1953-1958)

In 1952 Virginia Apgar, a physician at the Sloane Women’s Hospital in New York City, New York, created the Apgar score as a method of evaluating newborn infants’ health to determine if they required medical intervention. The score included five separate categories, including heart rate, breathing rate, reaction to stimuli, muscle activity, and color. An infant received a score from zero to two in each category, and those scores added up to the infant’s total score out of ten. An infant with a score of ten was healthy, and those with low scores required medical attention at birth.

Format: Articles

Subject: Technologies, Processes

"β-Catenin Defines Head Versus Tail Identity During Planarian Regeneration and Homeostasis" (2007), by Kyle A. Gurley, Jochen C. Rink, and Alejandro Sánchez Alvarado

Alejandro Sánchez Alvarado's laboratory group has employed molecular tools to investigate old questions about regeneration and as a result have identified some of the molecular mechanisms determining polarity. Recent work by his group has shown Wnt-β-catenin signaling determines whether a tail or a head will form during regeneration in planarians. This study was motivated by work Thomas Hunt Morgan conducted in the late nineteenth century.

Format: Articles

Subject: Experiments

Sonja Vernes, et al.'s Experiments On the Gene Networks Affected by the Foxp2 Protein (2011)

In 2011, Sonja Vernes and Simon Fisher performed a series of experiments to determine which developmental processes are controlled by the mouse protein Foxp2. Previous research showed that altering the Foxp2 protein changed how neurons grew, so Vernes and Fisher hypothesized that Foxp2 would affect gene networks that involved in the development of neurons, or nerve cells. Their results confirmed that Foxp2 affected the development of gene networks involved in the growth of neurons, as well as networks that are involved in cell specialization and cell communication.

Format: Articles

Subject: Experiments

Frog Embryo in the Blastula Stage

StageName: 8

Illustration of the animal-vegetal gradient in Xenopus laevis ( African clawed frog) eggs after fertilization. During fertilization, the sperm s point of entry determines the future dorsal side (shaded) and ventral side (unshaded) of the embryo. The prospective ventral side of the embryo forms on the side where the sperm enters while the prospective dorsal side forms opposite the sperm s point of entry.

Format: Graphics

"Risks and Benefits of Estrogen Plus Progestin in Healthy, Postmenopausal Women: Principal Results from the Women's Health Initiative Randomized Controlled Trial" (2002), by Jacques Rossouw et al.

In 2002, the Writing Group for the Women's Health Initiative Investigators published the article Risks and Benefits of Estrogen Plus Progestin in Healthy, Postmenopausal Women: Principal Results from the Women's Health Initiative Randomized Controlled Trial in The Journal of the American Medical Association.

Format: Articles

Subject: Publications

“Elective Induction of Labor” (1955), by Edward Bishop

In 1955, obstetrician Edward Bishop, a physician specializing in childbirth, published the article “Elective Induction of Labor,” in which he proposed the best conditions for pregnant women to elect to induce, or begin, labor. Elective induction of labor requires an obstetrician to administer a drug to help a pregnant woman to start her contractions, and to rupture the fluid-filled sac surrounding the fetus called the amniotic sac.

Format: Articles

Subject: Reproduction, Publications

"The Environment and Disease: Association or Causation?" (1965), by Austin Bradford Hill

In 1965, Austin Bradford Hill published the article “The Environment and Disease: Association or Causation?” in the Proceedings of the Royal Society of Medicine. In the article, Hill describes nine criteria to determine if an environmental factor, especially a condition or hazard in a work environment, causes an illness. The article arose from an inaugural presidential address Hill gave at the 1965 meeting of the Section of Occupational Medicine of the Royal Society of Medicine in London, England.

Format: Articles

Subject: Publications

Walter Jakob Gehring (1939-2014)

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.

Format: Articles

Subject: People

“Pelvic Scoring for Elective Induction” (1964), by Edward Bishop

In the 1964 article, “Pelvic Scoring for Elective Induction,” obstetrician Edward Bishop describes his method to determine whether a doctor should induce labor, or artificially start the birthing process, in a pregnant woman. Aside from medical emergencies, a woman can elect to induce labor to choose when she gives birth and have a shorter than normal labor. The 1964 publication followed an earlier article by Bishop, also about elective induction.

Format: Articles

Subject: Reproduction, Publications

"A molecular wound response program associated with regeneration initiation in planarians" (2012), by Danielle Wenemoser et al.

In 2012, a team of scientists across the US conducted an experiment to find the mechanism that allowed a group of flatworms, planarians, to regenerate any body part. The group included Danielle Wenemoser, Sylvain Lapan, Alex Wilkinson, George Bell, and Peter Reddien. They aimed to identify genes that are expressed by planarians in response to wounds that initiated a regenerative mechanism. The researchers determined several genes as important for tissue regeneration.

Format: Articles

Subject: Experiments

"A Series of Normal Stages in the Development of the Chick Embryo" (1951), by Viktor Hamburger and Howard L. Hamilton

The developmental stages of the chick embryo were examined by Viktor Hamburger and Howard L. Hamilton in "A Series of Normal Stages in the Development of the Chick Embryo," published in the Journal of Morphology in 1951. These stages were published to standardize the development of the chick based on varying laboratory conditions and genetic differences. The stages Hamburger and Hamilton assigned were determined by the visible features of the chick embryo.

Format: Articles

Subject: Experiments

Somites: Formation and Role in Developing the Body Plan

Somites are blocks of mesoderm that are located on either side of the neural tube in the developing vertebrate embryo. Somites are precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae. Somites also determine the migratory paths of neural crest cells and of the axons of spinal nerves.

Format: Articles

Subject: Processes

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