The mendelschen laws became in the 60's 19. Century of the scientifically interested Augustinermönch Gregor Mendel by crossing attempts at Erbsenpflanzen determines and ina first little considered publication formulated. Only over 1900 was confirmed these innovative realizations, brought with the Chromosomentheorie the transmission in connection and to the common property of the classical genetic science.
Table of contents
the mendelschen the laws or rules
the discoveries Mendels is based on statisticValues. Therefore they are called frequently also rules, with the reason that laws - differently than rules - would apply without reservation. Nevertheless they are well-known in the vernacular also as “Mendel pea equation”.
1. mendelsches law (uniformity law and/or.Reciprocity)
if two individuals of a kind (“parents “or Parentalgeneration P called) to be crossed with one another, in a characteristic, for which it pure-bend (homozygot) are, differ, then are the descendants of the first generation (“children” or first branch generation F1called) uniformly, i.e. both genotypisch and related to the phenotype directly. It is irrelevant, which represents the two individuals nut/mother or father. (Exception: The characteristic is on a Geschlechtschromosom (Gonosom). Then it can be that thoseF1 is not really uniform!)
2. mendelsches law (splitting law)
is crossed if the first descendant generation among themselves, then the individuals of the second generation (“grandchild “or second branch generation, F2) are no longer uniform, but point again thoseCharacteristics of the parents generation in certain numerical ratios up. There the uniformity is lost
- concerns it thereby dominance rezessive transmission, then three quarters form the dominant factor and a quarter the rezessive variant out (relationship of 3:1).
- of the 1 points second ) generation with intermediate transmission per a quarter of the descendants one of the two pure-curved variants and half of the individuals. Generation on (relationship by 1:2: 1).
3. mendelsches law (independence law/new combination law)
of two characteristics is separately from each other left, whereby starting from the 2. Generation (“grandchild”) new, pure-bends combinations to arise can. This law applies however then only if forthe characteristics responsible persons of genes on different Chromosomen sit (polyhybride hereditary courses). If the genes lie on the same Chromosomen, they are left in groups of couplings.
Mendel could do neither the term of the genes nor that of the Chromosomen. The actual nature of the hereditary factors was thus not well-known it. Only 1904 became by Suez clay/tone andBoveri the Chromosomentheorie of the transmission justifies. With the help of this theory the Mendelregeln can be explained without contradiction.
The Chromosomen are the units on those the hereditary factors (genes) to be passed on. (This explains the groups of couplings.) in the body cells the Chromosomen arise in pairs.Thus humans possess 23 Chromosomenpaare thus 46 Chromosomen. One speaks of a double Chromosomensatz. The Chromosomen are present in pairs in the body cell, because a Chromosom from the father and one from the nut/mother come. These two Chromosomen become also ashomologous Chromosomen designates. In a body cell the hereditary factors per characteristic are thus always doubly present.
With the formation of the sex cells the homologous Chromosomenpaare is separated. In an egg and/or one Spermium is thus only the simple Chromosomensatz. In a sex cellthe hereditary factors per characteristic are thus always once present. (The splitting rule becomes so understandable.) with fertilization thus the fusion of egg and Spermium to bring both sex cells in each case a hereditary factor per characteristic also. The body cell resulting from this fusion has thusagain the double Chromosomensatz. The hereditary factors can so again be combined. (Independence rule, free combination of the genes)
With large homogeneity of the genes of respective parents:
If A is dominance, each combination, which at least one A contains, has the appropriate characteristicthe parents AA. If AA stands for example for red blooms, and BB for blue blooms, and the gene for red blooms dominance is, have all “children” from AA and BB red blooms, but a quarter of the “grandchildren” again blue blooms.If none of the genes dominates, also mixtures develop - in this case possibly for lila blooms with the combination OFF.
If several genes on different Chromosomen result in together a characteristic, also completely new results can develop - for z. B. yellow blooms.The same applies to mutations.
The use of this recombination - thus the sexual Vermehrung - lies in the fact that more different gene combinations contribute to the evolution. Without sexual Vermehrung there would be only to a large extent identical copies from each organism. With sexual Vermehrung it givesa high range at descendants, and thus at survival strategies and - possibilities. To it comes that errors or weaknesses in hereditary property with sexual Vermehrung very much uneven on descendants distributed are - so that some descendants of clearly fewer problems have than their parents,and thus a reconciliation for errors when copying the heiress formations is created. Finally the sexual Vermehrung makes possible the assumption of the best characteristics of two occasionally separate populations into a common population and concomitantly a faster appropriation of abilities, those elsewherebefore already developed.
the mendelschen laws are used in particular in the animal and plant breeding, e.g. with the breed of hybrids. They can be used also for descending appraisals, e.g. in order to prove that did not determine humansas parents of a certain child are applicable. DNA.
which by Mendels theory not be explained could, became only understandably because of the Chromosomentheorie of the transmission. The genes for for example the stature height and fruit form of the tomatoes(A/a and/or. B/b) lie on the same Chromosom and therefore coupled to the germ cells are passed on. The germ cells can contain then only the combination OFF or off, not however off or off. 3. mendelsche rule must be limited therefore: Alleles are freely combinable, if the genes lie on different Chromosomen.
- H. Frederik Nijhout: The context macht's! Spektrum der Wissenschaft, April 2005, S. 70 - 77 (2005), ISSN 1702971
- biology book six-form high school Baden-Wuerttemberg class 9-10.
thus “everything” is written. (above in the text with reference)