Correlated responses in fitness and fertility traits were compared in transgenic and nontransgenic lines of mice selected for increased 8-week body weight. Two replicates of lines which either carried or did not carry the sheep metallothionein-1a sheep growth hormone transgene (oMt1a-oGH) were established. Host lines had been previously selected for rapid growth or selected randomly. Within-litter selection was carried out for 13 generations, and a randomly selected control line was kept for each set of replicate lines. Mice were genotyped every generation for the presence of the transgene, but this information was not used in selection decisions. The oMt1a-oGH construct was activated by adding 25 mM ZnSO 4 to the drinking water from 3 weeks (weaning) until 8 weeks of age. Zinc stimulation of the transgene was not carried out during mating, gestation and lactation. Correlated responses in fitness traits were measured by regression of least-squares means (as deviations from the control lines) on generation number. Two fitness indexes were defined to combine the information on individual fitness traits. The proportion of infertile matings was higher in generations 7 to 13 than in generations 0 to 6. Correlated responses to selection showed an increase in the cohabitation to littering interval in nontransgenic lines and an increase in litter sizes in lines from the selected background. Preweaning pup survival did not change over generations. Overall fitness increased in the transgenic line from the selection background whereas no changes were observed in the transgenic line from the control background. The initial frequency of 0.5 of the transgene was reduced to less than 0.10 in the selected background, but increased to an average of 0.62 in the control lines. The comparison of specific mating groups involving transgenic and nontransgenic mates revealed that the only consistent disadvantage in having a transgenic parent was the increase in the length of the cohabitation to littering interval. Major fitness problems were not associated with the oMt1a-oGH transgene, which makes this construct a potential choice for use in livestock breeding programmes.
Zusammenfassung
Korrelierte Verä nderungen bei den Merkmalen Fertilitä t und Fitness bei auf erhö htes 8-Wochengewicht selektierten Stä mmen von oMt1a-oGH transgenen Mä usenKorrelierte Reaktionen der Merkmale Fertilität und Fitness wurden bei transgenen und nicht transgenen Mäuselinien verglichen. Es wurden zwei Nachzü chtungen von Linien erstellt, die entweder das ovine Metallothionein-1a Wachstumshormon transgen tragen bzw. es nicht tragen. Zuvor waren Wirtslinien entweder auf schnelles Wachstum selektiert oder zufällig ausgesucht worden. Die Selektion erfolgte innerhalb der Wü rfe auf erhö htes 8-Wochengewicht fü r 13 Generationen, und eine zufällig selektierte Kontroll-Linie wurde fü r jede der replizierten Linien gehalten. In jeder Generation wurden die Mäuse auf die Anwesenheit des Transgens genotypisiert, aber diese Information wurde nicht fü r Selektionsentsche...