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ru>JJMC89 bot III: Moving :Category:Obsolete biological theories to :Category:Obsolete biology theories per Wikipedia:Categories for discussion/Speedy

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Moving Category:Obsolete biological theories to Category:Obsolete biology theories per Wikipedia:Categories for discussion/Speedy

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The '''bead theory''' is a disproved [[hypothesis]] that [[gene]]s are arranged on the [[chromosome]] like [[bead]]s on a [[necklace]]. This theory was first proposed by [[Thomas Hunt Morgan]] after discovering [[Gene|genes]] through his work with breeding red and white eyed fruit flies.<ref>{{Cite journal|last=Morgan|first=Thomas Hunt|date=1910|title=Sex Limited Inheritance in Drosophilia|url=http://www.esp.org/foundations/genetics/classical/thm-10a.pdf|journal=Science|volume=32|issue=812|pages=120–122|via=ESP.org|doi=10.1126/science.32.812.120|pmid=17759620|bibcode=1910Sci....32..120M}}</ref> According to this theory, the existence of a gene as a unit of inheritance is recognized through its mutant alleles. A mutant allele affects a single phenotypic character, maps to one chromosome locus, gives a mutant phenotype when paired and shows a Mendelian ratio when intercrossed. Several tenets of the bead theory are worth emphasizing :-
1. The gene is viewed as a '''fundamental unit of structure''', indivisible by crossing over. Crossing over take place between genes ( the beads in this model ) but never within them.
2. The gene is viewed as the '''fundamental unit of change or mutation'''. It changes in toto from one allelic form into another; there are no smaller components within it that can change.
3. The gene is viewed as the '''fundamental unit of function''' ( although the precise function of gene is not specified in this model ). Parts of a gene, if they exist cannot function. [[Guido Pontecorvo]] continued to work under the basis of this theory until
[[Seymour Benzer]] showed in the 1950s that the bead theory was not correct.<ref>{{Cite journal|last=Siddoqi|first=Obaid|date=1999|title=Guido Pontecorvo (1907-1999)|journal=Journal of Genetics|volume=78|issue=3|pages=171–173|doi=10.1007/BF02934463|s2cid=31960838}}</ref> He demonstrated that a gene can be defined as a unit of function. A gene can be subdivided into a linear array of sites that are mutable and that can be recombined. The smallest units of mutation and recombination are now known to be correlated with single nucleotide pairs.

==References==
*
<references />
* {{cite journal | author=BENZER S | title=Genetic fine structure and its relation to the DNA molecule | journal=Brookhaven Symp Biol | year=1956 | pages=3–5 | issue=8 | pmid = 13293416 }}
* An Introduction to Genetic Analysis 7th edition Griffiths AJF, Miller JH, Suzuki DT, et al.
New york W.H. Freeman;2000
[[Category:Obsolete biology theories]]
[[Category:Genetics]]

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Bead theory - История изменений

Admin: 1 версия импортирована

ru>JJMC89 bot III: Moving :Category:Obsolete biological theories to :Category:Obsolete biology theories per Wikipedia:Categories for discussion/Speedy