ISSN:
1573-6857
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract Grell's (1964) “non-competitive” data describing segregation of markers on two non-homologous, non-crossover chromosomes inDrosophila melanogaster, called Dp and 4, are explained on the basis of the “elastica” but also on the chance of the two becoming associated with each other. According to the model,early in meiosis the chance that two chromosomes pair with each other at the (terminal) centromeres and telomeres, p1, is an inverse function of difference in their lengths (the Dp chromosome's length, called LDp, was different in different flies, whereas that of the non-exchange 4 was the same throughout). If these two chromosomes, once paired, are not approximately equal in length, thenlate in meiosis as they both spiralize and stiffen, their ends tend to separate as predicted by the elastica, thus preventing co-orientation and bringing about elevation of the % Dp, 4 non-disjunction. Such paired chromosomes are compared with the form of the elastica describing a strung (arrow) bow. That is, beginning with a string and bow of equal lengths and allowing the string to become shorter (Dp shorter than 4), moments at the paired centromeres and/or telomeres would increase much more rapidly than if the bow becomes longer (Dp longer than 4), the model predicts that the former rate of increase is the square of the latter, in good agreement with the data. Other experimental results are also consistent with those predicted by the elastica. In “competitive” data with three non-crossover, non-homologous chromosomes, T (also constant in length) Dp and 4, the following T, Dp: T, 4: Dp, 4 non-disjunction ratios are easily explained on the basis of a random Markov (stochastic) process hypothesizing three steps between pairing and M1: 2/3:: 1/6 : 1/6 at LDp=0.3, 2/5 : 1/5 : 0 at LDp=0.9, 1/6 : 1/2 : 0 at LDp=1.4 and 1/6 : 2/3 : 1/6 at LDp=3.0.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF02324471
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