Published online by Cambridge University Press: 14 April 2009
Variability in fertility in compound chromosome (CC) strains of Lucilia cuprina (Wiedemann) is directly correlated with the segregation properties of the CCs in those strains. In compound fifth-chromosomes, high fertility (up to 50% ) is associated with high frequencies of segregation of the left element (C(5L)) from the right element (C(5R)) in males, while low fertility (up to 25%) is associated with random assortment of the CCs in males. Regular segregation of C(5L) and C(5R) chromosomes in males is associated with particular C(5L) elements, which contain cytologically visible duplications of 5R chromatin. These duplications may contain a site which is normally involved in the pairing of the fifth chromosomes in males.
In females the CCs segregate from one another with a frequency of 89%. None of the C(5R) elements studied affected segregation in males, and neither C(5L) nor C(5R) elements had any demonstrable effect on segregation in females. Transmission of certain CC elements through one or both sexes is significantly lower than expected. This could have a variety of causes, such as meiotic drive, inviability associated with position effects, or homozygosis of deleterious mutations on homologous CC arms during meiotic crossing over in females. The CC strains released during a field trial of genetic control contained both high-fertility and low-fertility C(5L) chromosomes. Both types of CC were subsequently recovered from individuals which had overwintered in the field. Over a period of several generations following this recolonization one particular high-fertility C(5L) chromosome increased in frequency to near-fixation, despite the presence in this chromosome of deleterious mutations.
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