| 释义 |
polytene, a. Cytology.|ˈpɒlɪtiːn|
[poly- + -tene.]
Applied to giant chromosomes found in certain interphase nuclei, esp. in dipterous insects, and composed of many parallel copies of the genetic material, in which the active regions may be identifiable microscopically.
1935P. C. Koller in Proc. R. Soc. B. CXVIII. 372 We can regard these chromosomes as corresponding with paired pachytene chromosomes at meiosis in which the intercalary parts between chromosomes have been stretched and separated into smaller units, and in which, instead of two threads lying side by side, we have 16 or even more. Hence they are ‘polytene’ rather than pachytene; I do not, however, propose to use this term; I shall refer to them as ‘multiple threads’. 1959C. M. M. Begg Introd. Genetics iii. 27 The specificity of this pairing [of homologous chromosomes] is shown very strikingly in the case of the exceptional polytene threads of the much enlarged salivary gland nuclei of Diptera. 1971Nature 21 May 184/2 Individuals of the species which breeds in freshwater can only be identified with certainty by the banding patterns of their polytene chromosomes. 1976Bell & Coombe tr. Strasburger's Textbk. Bot. (rev. ed.) 31 (caption) Giant chromosome, polytene and consisting of about 2048 strands, from the suspensor of the embryo of Phaseolus vulgaris.
Hence polytenic |-ˈtiːnɪk| a., in the same sense; ˈpolyteny, the state of being polytene; also ˌpolyteniˈzation, the production of polyteny; polyˈtenized ppl. a. (of a chromosomal constituent) reduplicated owing to the polyteny of the chromosome.
1942Proc. R. Soc. Edin. B. LXI. 318 The degree of polyteny found in the tissues of a dipteran larva varies with the species. 1953W. Hovanitz Text-bk. Genetics vii. 100 The terms salivary chromosomes and polytenic chromosomes have been applied to them [sc. giant chromosomes]. 1958Polyteny [see mixoploidy]. 1966Proc. R. Soc. B. CLXIV. 280 After many steps of polytenization (12 or 14 consecutive replications) such a labelled chromosome thread may still extend as a single linear unit from the one end of the giant chromosome to the other end. 1968H. Harris Nucleus & Cytoplasm iv. 77 The chromosomes in these [salivary] glands are extraordinary for two reasons. The first is that they are grossly polytenic. Each chromosome contains thousands of identical parallel copies of the basic diploid genetic structure. The extent of polyteny may vary in different species, but for Chironomus tentans it has been estimated that each chromosome contains about 16000 times the normal diploid amount of DNA. 1974Nature 29 Mar. 446/1 Mutational data also rule out simple polyteny and polyploidy, where every single gene on every chromosome is polytenised or where every chromosome is present in two or more copies. 1976Ibid. 17 June 614/2 Ciliata and Diptera..show a high tendency for endopolyploidisation and polytenisation. 1976Bell & Coombe tr. Strasburger's Textbk. Bot. (rev. ed.) 31 In rare cases repeated multiplication of chromonemata leads to multistranded (polytenic), cable-like, giant chromosomes. |