Variation in Scutellar Bristle Number an Alternative Hypothesis

Robertson, Alan

doi:10.1086/282345

Cited by 25 publications

(11 citation statements)

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“…In establishing the relationship between genotype and phenotype for a canalised system Rendel has made extensive use of the probit transformation. Robertson (1965) has argued that this may lead to incorrect inferences about the nature of the canalisatiori zone if scutellar bristle development is not a sequential or cumulative process as was assumed by Rendel. Robertson raised the possibility that the probabilities of bristle formation at the anterior and posterior sites could be modified independently.…”

Section: /3-u (Iii) Posterior Bristle Selectionmentioning

confidence: 99%

“…Rendel's model assumed that total scutellar bristle number is the primary character under control of the single developmental variable. Robertson (1965) argued that the formation of 4 bristles may not be a sequential or cumulative process and suggested that total scutellar bristle number is a function of developmental events at the individual sites which may be independent in any given individual. By varying the dose of a series of scute alleles, Scowcroft et al (1968) found that a single developmental scale does not adequately describe the phenomenon of canalisation of total scutellar bristle number.…”

Section: Introductionmentioning

confidence: 99%

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Scutellar bristle components and canalisation in Drosophila melanogaster

Scowcroft

1973

Heredity

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SUMMARYSelection was applied to anterior and posterior scutellar bristles separately and jointly in two populations, one of which straddled the 3/4 bristle threshold and the other the 4/5 bristle threshold. The object was to define the thresholds of the normally canalised 4 bristle phenotype in terms of the component anterior and posterior bristles. Changes in total bristle number (anteriors plus posteriors) at the 3/4 threshold is a function of addition or loss of bristles at the posterior site, whereas changes at the 4/5 threshold exclusively involve anterior bristles. It is concluded that the component anterior and posterior bristles are essentially independent.

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Section: /3-u (Iii) Posterior Bristle Selectionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Scutellar bristle components and canalisation in Drosophila melanogaster

Scowcroft

1973

Heredity

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“…Because of the difficulty of suggesting an explanation within this framework, consideration was given to the relevance of bristle position on the scutellum, because Robertson (1965), Scowcroft et al (1968), Scowcroft (1970), andScowcroft (1973) have questioned the validity of using total scutellar bristle number to analyse changes in canalization of the character (see Appendix 2).…”

Section: Occurrence Of Canalization At 2 Scutellar Bristlesmentioning

confidence: 99%

Studies on the Scutellar Bristles of Drosophila melanogaster. IV. Selection for Low Bristle Number in Oregon-RC Wild-type Lines

Sheldon¹,

Evans²

1984

Aust. Jnl. Of Bio. Sci.

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Results are presented of 130-145 generations of selection for low scutellar bristle number in four lines of D. melanogaster derived directly from an Oregon-RC wild-type stock and in one derived from an Oregon-RC line selected for low sternital bristle number. The most rapid initial response and the lowest mean scutellar bristle number ultimately reached, just below 2 bristles, occurred in a line in which the response was due to a new recessive gene located at approximately 17·4 on the X chromosome. Three of the other four lines reached a plateau just above a mean of 2 bristles after different patterns of response. These plateaux reflected a new canalization or threshold phenomenon at 2 bristles in these lines. The remaining line reached a mean of about 2· 5 bristles after some 50 generations and remained at that level or slightly higher thereafter, but had no indication of canalization at 2 bristles. Two relaxed lines were derived from each selection line at different times and showed variable patterns of regression towards the base population level.In the early generations of selection, as the mean bristle number slowly dropped below the canalized wild-type level of 4 bristles, flies with more than 4 bristles continued to appear, i.e. the probit width of the 4-bristle class tended to drop from its un selected level of 5·4-5·8". to quite low levels in the selection lines and to recover in the relaxed lines as their mean bristle number moved back towards the un selected level. This could not be interpreted in the same way as similar phenomena in highselection lines, i.e. selection of poor regulators of the scute locus. Other possible explanations for these results and for the new canalization observed at 2 bristles were considered without being able to accommodate them fully within a modified model of regulation of the scute locus. The most likely possibility seems to be that the low selection response is due to selection of less-efficient alleles of a gene which is the inducer of the scute locus. A large reduction in the degree of dominance of sc+ over scute (SCi) was also observed in these selection lines, which may be compatible with the above explanation.Correlated responses in sternital bristle number in the selection and relaxed lines, while generally positive, were not closely related to the pattern of change in scutellar bristles. The dominance of sc+ over SCi in respect of sternital bristles showed little change except in one line where it increased, while dominance in respect of scutellar bristle score decreased.

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“…In ADC-7, BAB has some positional decanalization, and ABB is clearly positionally and numerically decanalized. (R OBERTSON , 1965) ; it could be due to a different temporary determination of the chaetogen production in each site (P OODRY , 1975).…”

mentioning

confidence: 99%