The genetics of recombination / D.G. Catcheside.

  • Catcheside, D. G.
Date:
[1977]
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The genetics of recombination / D.G. Catcheside. Source: Wellcome Collection.

    30/192 (page 16)
    16 Recombination in eucaryotes nucleus, the only diploid nucleus in the life cycle. Shortly the diploid nucleus undergoes meiosis to produce a linear row of four nuclei ; each of which then divides again mitotically to produce a row of eight. A spore is formed around each nucleus. When the ascus is ripe it contains a linear row of ascospores that are related by descent to the divisions at meiosis. Apart from rare accidents which cause spores to be misplaced, the ordered ascus is therefore a complete record of the events at meiosis. The theory of analysis was treated earlier (pp. 2-6). Further consideration will be restricted to information bearing on the mechanism of recombination by crossing over and conversion and therefore on the analysis of events in short sections of chromosomes. The two loci ad-3A and ad-3B are close together (recombination less than 0.5%) in the right arm of linkage group I (Fig. 2.2a). Mutation in either try-2 - - al-2 ■■ nic-2 -• ad-3B \ ad-3A ^ 43 his-2 ; : 0-46 I 8-4 36 pan-2 72 -I- 5^ 23 pan-2 ylo • • 7 7 Ì 1-7 ad-1 0-2 I ylo ■ • 013 004 0-14 OOOt 64 -- 15 +■ 38 cys 9 -- N Л 1-7 1-9 0008 0006 0012 pan-1 ■ • P152 f P24 f me-2 H98 -H PI 40ч K44- K43- KIS' ^0 11 0001 0 001 try-4 0 004 0015 0011 lys-5 ■ • mt (a) (b) (c) (d) Figure 2,2 Neurospora crassa linkage maps of regions in which recombination in short segments is analysed in the text. The maps include magnified fine structure maps of pan-2, cys and me-2, in which the metric used is the percentage frequency of prototrophic recombinants. Other distances are in centimorgans. (a) Linkage group I: al-2, albino-2', nic-2, nicotinamide-2', ad-3B, adenine-ЗВ', ad-3A, adenine-SA ; his-2, histidine-2; mt, mating type. (b) Linkage group VI, chiefly right arm; try-2, tryptophan-2; pan-2, pantothenate-2; ad-1, adenine-1-,ylo,yellow. (c) Linkage group VI, chiefly left arm: pan-2, pantothenate-2', ylo, yellow, cys, cysteine ; lys-5, lysine-5. (d) Linkage group IV, right arm: pan-1, pantothenate-1 ; me-2, methionine-2; try-4, tryptophan-4.