| 释义 |
▪ I. † ˈmorgan1 Obs.
(See quot.)
1659Fuller App. Inj. Innoc. i. 65 There were lately false twenty-Shilling pieces, (commonly called Morgans,) coined by a cunning and cheating Chymist.
▪ II. morgan2 Now dial. (Sussex, Hants).|ˈmɔːgən|
Also 9 margon, margin (E.D.D.).
[See marg.]
A name for various species of camomile (Anthemis); also applied to the Ox-eye Daisy, Chrysanthemum Leucanthemum.
1669Worlidge Syst. Agric. (1681) 189 Mugwort, Morgan, Wormwood,..or other bitter or noisome Weeds or Herbs. a1722Lisle Husb. (1757) 448, I filled my meads with morgan and other trumpery. 1847Halliwell, Margan, the stinking camomile. 1886Britten & Holland Eng. Plant-n. 341 Dutch Morgan, Chrysanthemum Leucanthemum. 1892Times 15 Feb. 12/1 A large number of ewes are said to have aborted in one farm in Hampshire through being fed on hay containing ‘morgan’ or ‘hay weed’.
▪ III. morgan4 Genetics.|ˈmɔːgən|
[named after Thomas Hunt Morgan (see Morganism).]
A unit of the relative distance on a chromosome between two linked genes, defined in terms of the frequency of crossing-over between them so that the distance in morgans between two genes is equal to this frequency when they are close enough together for the effect of multiple crossing-over to be negligible. (Sometimes used for one hundredth of this unit.)
1919J. B. S. Haldane in Jrnl. Genetics VIII. 305 Let x be the distance between the loci of two factors, y their cross-over value, and let the unit of distance be chosen so that when y is sufficiently small x becomes equal to y... The value of y for a given value of x is the sum of the probabilities of all odd numbers of cross-overs. {ergo}y = ..½ (1 - e-2x)... It is suggested that the unit of distance in a chromosome as defined above be termed a ‘morgan’, on the analogy of the ohm, volt, etc. Morgan's unit of distance is therefore a centimorgan. Ibid., The cross-over values ·412 and ·236 correspond, according to curve (c),..to distances of ·549 and · 261 morgans respectively. 1965J. A. Serra Mod. Genetics I. vii. 260 Map distances between gene loci are the cross-over values expressed as percentages of recombination for small intervals. Thus, 1% of recombination is often called one cross-over unit..or a centimorgan... One morgan is equal to 100 centimorgans. [Note] Some authors call a cross-over unit one morgan. 1971Levitan & Montagu Textbk. Human Genetics ix. 376 Each morgan is divisible into 100 centimorgans, each centimorgan corresponding to the map distance between two loci showing 1 per cent crossing over between them. For close loci the crossover percentage can be translated directly into centimorgans, but this is not possible for more distant loci, especially those more than 30 centimorgans apart. 1971Nature 24 Dec. 475/1 Pedigree studies by Lawler and her co-workers established a close linkage (0·03 morgans) between Rh, the rhesus set of blood group loci, and one of the loci, El1, that can lead to elliptocytosis of the red cell. |