9/25/2023 0 Comments Zmatrix not for use by womenThe NFR/N strain is an example of an inbred high-breeder strain, while common C57BL strains normally produce lower numbers of litters and are often denoted “moderate breeders.” Females of the NFR/N strain are known to produce several large litters during a long period of time. Such strains are often denoted “high breeders,” and they carry genes ensuring large litter size, high stress resistance during pregnancy, and good nursing properties during the lactation period. However, some strains of mice have, after many years of selection, become more resistant to different types of stress and produce large litters in most types of environments. In research there is often a considerable problem when there is a low reproductive performance of genetically modified model mice. This discrepancy can be due to differences in more or less definable environmental factors, such as differences in cages, food, bedding material, routines, health status, and handling of the mice. Most scientists who have worked with mice in different animal houses have experienced that the same inbred strains can show different reproductive performance. These factors are normally very complex and are often difficult to define. REPRODUCTIVE success in mice, as in all mammals, is dependent on several environmental and genetic factors. It is well known that reproductive performance is polygenically controlled, and the identification of the major loci in this complex process opens the possibility of investigating the natural genetic control of reproduction. A locus on chromosome 1 affecting maternal body weight was also identified and has been denoted Bwq7. Furthermore, on chromosomes 13 and 17 we found loci ( Pregq3 and Pregq4) influencing the outcome of allogeneic pregnancy (allogeneic by means of MHC disparity between mother and fetuses). On chromosome 11 two loci affecting the pregnancy rate ( Pregq1 and Pregq2) were identified. The neonatal growth phenotype was affected by Fecq3 and a locus on chromosome 9 ( Neogq1). Loci controlling litter size were detected on chromosomes 1 ( Fecq3) and 9 ( Fecq4). A predetermined number of phenotypes related to reproductive performance were recorded, and these included litter size, neonatal growth, and pregnancy rate. Each of the 237 females of the N2 generation was allowed to mate twice with MHC-congenic B10.RIII (H-2r) males and twice with B10.Q males. The moderate breeder chosen for F 1 and N2 progeny was B10.Q, which is a genetically well-characterized MHC-congenic mouse of the H-2q haplotype. The high-breeder mouse strain we used is the inbred NFR/N mouse (MHC haplotype H-2q), which has extraordinary good breeding properties. We have identified polymorphic microsatellite markers for the mouse strains used and performed a genomewide scan on 237 females from a gene-segregating backcross between a high breeder and a relatively poor breeder. In this study we have focused on the identification of genetic regions, quantitative trait loci (QTL), which affect the breeding capacity of female mice. Both environmental and genetic factors can dramatically affect reproductive performance in mice.
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