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M J Merrick

Publications and source records attributed to M J Merrick.

22 records · Page 2Linked to original sources
PubMed1975

The inheritance of penicillin titre in wild-type isolates of Aspergillus nidulans.

In a sample of 52 wild-type isolates of Aspergillus nidulans, penicillin titre ranged from 0-0 to 14-4 units/ml. These differences in titre were under genetic control. Most of the variation between isolates was attributable to differences between heterokaryon-compatibility groups although significant differences were also found within groups. Genetic variation for penicillin titre was observed among the progeny in four of seven crosses between wild-type isolates. In these four crosses the variation was continuous, indicating that this is a polygenically determined character, and progeny with titres superior and inferior to those of the parents were produced. The genes determining penicillin production are predominantly additive in their action. Crosses between heterokaryon-incompatible isolates generated more genetic variation than those involving compatible parents, supporting the hypothesis that heterokaryon-compatible isolates are frequently closely related.

Analysis of Variance↗
PubMed1975

Hybridization and selection for increased penicillin titre in wild-type isolates of Aspergillus nidulans.

Repeated hybridization and selection among wild-type isolates produced strains of Aspergillus nidulans with increased penicillin titre. Four independent selection lines were established, each originating from a sexual cross between two different heterokaryon-incompatible wild-type isolates. In each generation, two selected high-titre sister strains were crossed to produce the next generation. An initial increase in titre was obtained in each line, but after four or five generations of selection the genetic variation was considerably reduced and the rate of response to selection had decreased. From a base population of wild-type isolates with a mean titre of 8-6 units/ml the progeny mean titre was raised to between 16 and 20 units/ml in each line. The gradual nature of the response suggests that a number of genes determine penicillin titre in the wild-type isolates used. The gene action throughout the selection programme was predominantly additive.

Aspergillus nidulans↗
PubMed1975

The inheritance of penicillin titre in crosses between lines of Aspergillus nidulans selected for increased productivity.

Selection for increased penicillin production among the progeny of pairwise crosses between wild-type isolates of Aspergillus nidulans resulted in the production of high-titre strains. Three crosses were made between strains with increased titre derived from independent selection lines. Significant genetic variation was found among the progeny of each cross, indicating that different genes for increased titre had been selected in each line. Gene action was additive in each cross. Renewed selection from the progeny of one 'between-line' cross resulted in further increases in titre, over three successive generations.

Aspergillus nidulans↗