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In biology a population is all the organisms of the same group or species, which live in a particular geographical area. The area of a sexual population is the area where inter-breeding is potentially possible between any pair within the area, and where the probability of interbreeding is greater than the probability of cross-breeding with individuals from other areas.
Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic, meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.
A multiple birth is the culmination of one multiple pregnancy, wherein the mother delivers two or more offspring. A term most applicable to vertebrate species, multiple births occur in most kinds of mammals, with varying frequencies. Such births are often named according to the number of offspring, as in twins and triplets. In non-humans, the whole group may also be referred to as a litter, and multiple births may be more common than single births. Multiple births in humans are the exception and can be exceptionally rare in the largest mammals.
Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in [[behavioral genetrom biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.
Eugen Fischer was a German professor of medicine, anthropology, and eugenics, and a member of the Nazi Party. He served as director of the Kaiser Wilhelm Institute of Anthropology, Human Heredity, and Eugenics, and also served as rector of the Frederick William University of Berlin.
A grid illusion is any kind of grid that deceives a person's vision. The two most common types of grid illusions are the Hermann grid illusion and the scintillating grid illusion.
Paul Emil Flechsig was a German neuroanatomist, psychiatrist and neuropathologist. He is mainly remembered today for his research of myelinogenesis.
Pregnancy over the age of 50 has, over recent years, become possible for more women, and more easily achieved for many, due to recent advances in assisted reproductive technology, in particular egg donation. Typically, a woman's fecundity ends with menopause, which, by definition, is 12 consecutive months without having had any menstrual flow at all. During perimenopause, the menstrual cycle and the periods become irregular and eventually stop altogether, but even when periods are still regular, the egg quality of women in their forties is lower than in younger women, making the likelihood of conceiving a healthy baby also reduced, particularly after age 42. It is important to note that the female biological clock can vary greatly from woman to woman. A woman's individual level of fertility can be tested through a variety of methods.
Wilhelm Weinberg was a German obstetrician-gynecologist, practicing in Stuttgart, who in a 1908 paper, published in German in Jahresheft des Vereins für vaterländische Naturkunde in Württemberg, expressed the concept that would later come to be known as the Hardy–Weinberg principle.
The Autobahn is the federal controlled-access highway system in Germany. The official German term is Bundesautobahn, which translates as "federal motorway". The literal meaning of the word Bundesautobahn is "Federal Auto(mobile) Track".
Felix Bernstein, was a German Jewish mathematician known for proving in 1896 the Schröder–Bernstein theorem, a central result in set theory, and less well known for demonstrating in 1924 the correct blood group inheritance pattern of multiple alleles at one locus through statistical analysis.
Curt Stern was a German-born American geneticist.
Nancy L. Segal is an American evolutionary psychologist and behavioral geneticist, specializing in the study of twins.
Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" connotes a focus on genetic influences, the field broadly investigates genetic and environmental influences, using research designs that allow removal of the confounding of genes and environment. Behavioural genetics was founded as a scientific discipline by Francis Galton in the late 19th century, only to be discredited through association with eugenics movements before and during World War II. In the latter half of the 20th century, the field saw renewed prominence with research on inheritance of behaviour and mental illness in humans, as well as research on genetically informative model organisms through selective breeding and crosses. In the late 20th and early 21st centuries, technological advances in molecular genetics made it possible to measure and modify the genome directly. This led to major advances in model organism research and in human studies, leading to new scientific discoveries.
Erik Gustav Elfving was a Finnish mathematician and statistician. In statistics, he wrote pioneering papers about the optimal design of experiments. He made other notable contributions to the mathematical sciences and to Finnish universities.
Sinistrin is a naturally occurring sugar polymer or polysaccharide, also known as polyfructosane. It belongs to the fructan group, like inulin. As it is the case with similar substances, such as fructans or inulin, sinistrin acts as an energy storage molecule in plants.
Max Westenhöfer was a German pathologist and biologist who contributed to the development of the anatomic pathology and the reform of public health in Chile.
Peter Propping was a German Human geneticist.
In adoption studies, selective placement refers to the practice by which adoption agencies tend to deliberately match certain characteristics of an adopted child's adopted parents with those of his or her biological parents. When this occurs, it results in a correlation between environments between biological relatives raised in different homes. It has the potential to bias the conclusions of such studies, because twins who were reared in separate environments may in fact have been reared in much more similar environments than assumed. This can result in an inflated estimate of heritability. There is evidence that selective placement was a major confound in many early studies of twins reared apart. Some adoption studies report little or no evidence of selective placement. For example, a 1979 study by Ho et al. reported a generally low level of selective placement in adopted children for either physical or behavioral traits. The authors concluded that to the extent that selective placement occurred for such traits, "our data suggest that it is based largely on characteristics of the birth father," rather than those of the adoptee. Carey (2003) concluded that selective placement was "moderate" for physical characteristics and typically "small or nonexistent" for behavioral characteristics.
References
- Fellman, Johan; Eriksson Aldur W (Apr 2009). "Statistical analyses of Hellin's law". Twin Research and Human Genetics. Australia. 12 (2): 191–200. doi:10.1375/twin.12.2.191. ISSN 1832-4274. PMID 19335191.
- Fellman, Johan; Eriksson Aldur W (Apr 2009). "On the history of Hellin's law". Twin Research and Human Genetics. Australia. 12 (2): 183–90. doi:10.1375/twin.12.2.183. ISSN 1832-4274. PMID 19335190.
- Fellman, John (Dec 2017). "Aspects of the History of Twin Research: Statistical Congresses in the 19th Century and Hellin's Law". Twin Research and Human Genetics. 21 (1): 57–66. doi: 10.1017/thg.2017.68 . PMID 29258629.
- Hellin, D. (1895). Die Ursache der Multiparität der uniparen Tiere überhaupt und der Zwillingsschwangerschaft beim Menschen insbesondere. München: Seitz und Schauer. p. 25.
Während man sagen kann, dass beim Menschen durchschnittlich eine Zwillingsgeburt auf etwa 89 einfache Geburten vorkommt tritt eine Drillingsgeburt auf (89)2 einfache Geburten auf, eine Vierlingsgeburt auf (89)3; überhaupt, soweit dies in Grenzen der Möglichkeit liegt, erscheint eine x fache Geburt auf (89)x–1 einfache Geburten.
- Zeleny, Charles (Mar 1921). "The Relative Numbers of Twins and Triplets". Science. 53 (1368): 262–263. Bibcode:1921Sci....53..262Z. doi:10.1126/science.53.1368.262. PMID 17794418.
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