A resource family of pigs has been constructed by using a boar of Göttingen miniature pig and two sows of Meishan pig as parents. In the construction of the family, two F1 males and 18 F1 females were intercrossed to generate 143 F2 offspring. The members of the family were genotyped using 243 genetic markers including 26 markers developed in our laboratory in order to generate a linkage map of markers for use in detecting quantitative trait loci (QTLs) in the family. The markers consisted of 237 microsatellites, five PRE-1 markers, and one RFLP marker. The linkage map was revealed to cover all 18 autosomes and the X chromosome; and the total length of the sex-averaged linkage map was calculated to be 2561.9 CM. Four out of the 26 markers developed in our laboratory exended the current linkage map at the termini of chromosomes 1p, 5p, 11p, and Xq. The linkage maps of all the chromosomes except for chromosome 1 were found to be longer in females than in males. Concerning chromosome 1, the length of the linkage map showed no difference between females and males, which was attributed to low recombination rates between markers localized in the centromeric region in females. The average ratio of female-to-male recombination was calculated to be 1.55.

Introduction: The acrosin gene (ACR) has been assigned to the terminal region of swine chromosome 5 p‐arm, p15, by fluorescence in situ hybridization1. The aconitase gene (ACO2) was assumed to map to the p telomeric region of chromosome 5, on the basis of its position in linkage map1,2. In order to explore the arrangement of ACO2 and ACR on the chromosome and in the linkage map, we have molecularly cloned porcine genomic fragments containing at least a part of the ACO2 and ACR genes.

Type conversions among the three types, P, Q and M, of the P-M hybrid dysgenesis in Drosophila melanogaster were examined. Among 54 isofemale lines established from two natural populations , about 30% of the lines have shown type conversions during laboratory culture for two years. These were M-~Q, Q-~M, P-~Q and P-+M in order of frequency. In hybrid lines (HMP) started from M x P crosses, flies receiving a P type chromosome rapidly changed their cytotype away from the M toward the P or the Q type . However, in flies consisted of only M strain-derived chromosomes, cytotype conversions were comparatively slow. Similarly, P factor activities of hybrid lines increased with generation number in flies having a P type chromosome in the genome but not in flies without it. M strain-derived chromosomes were isolated to make the HMP[e] series after several generations of exposure to the P type chromosome. In these series, P type lines appeared when the P type chromosome was removed in early generations of the HMP lines. P factors did not increase, however, with the same procedures in the later generations of the HMP lines. Circumstances related to type conversions in the P-M system were discussed: (1) P and Q factors and the M states must coexist in a genome and even in one chromosome. (2) P and Q factors or cytotype determinants transpose on a certain cytotype background.(3) How do the interactions between P or Q factors and cytotypes lead to expression of dysgenic traits?