The Ovarian Teratoma Mapping Method in the Mouse

Murine ovarian teratomas were used to determine recombination percentages for gene-gene and centromere-gene intervals. Data were obtained utilizing a recombinant inbred strain, LTXBJ, and a number of newly developed LT/SvEi congenic strains. --Centromere-gene recombination was measured at 11.3 & 1.2% for the centromere of chromosome 7 Gpi-1 interval and 15.8 2 2.4% for the centromere of chromosome 14 Np-1 interval using the ovarian teratoma method. The centromere Np-1 interval was measured at 26.5 f 3.6% using a standard backcross involving the RbGBnr Robertsonian translocation as a centromere marker. --To assess the accuracy of the ovarian teratoma mapping method, we compared the recombination frequency obtained for the Mpi-lMod-1 interval on chromosome 9 using the ovarian teratoma method to that obtained using a standard backcross. The recombination percentage was 22.9 & 5.4 using the ovarian teratoma method and 18.6 & 3.3 using the backcross method, indicating that the two methods produce equivalent estimates of recombination. In addition, for centromere-gene intervals known to be more than 30 cM in length, the ovarian teratoma method was cmsistent with classical recombination methods, yielding high recombination percentages. We conclude from these results that the ovarian teratoma mapping method is a reliable method for estimating recombination frequencies and the most accurate method available for estimating centromere-gene recombination frequency in the mouse. LTHOUGH more than 450 genes have been positioned on the chromosome A map of the laboratory mouse, one region on each of the chromosomes remains poorly defined in terms of recombination frequency: the region between the centromere and nearby genes. To date, two methods have been used to estimate centromere-gene recombination percentages. One method uses cytological centromere markers, such as Robertsonian translocations or centromeric heterochromatin polymorphisms, as codominant genetic (centromeric) markers in conventional linkage crosses (CATTANACH and MOSELEY 1973; LYON, BUTLER and KEMP 1968; EICHER et al. 1977; DAVISSON and RODERICK 1975). The centromere-gene recombination percentages obtained using Robertsonian translocations are suspect, however, because these chromosomal aberrations often cause disturbances in the crossing over process. In addition, the effect of Robertsonian translocations on recombination may depend on the chromosomes involved, the origin of the Robertsonian chromosome or both (CATTANACH and MOSELEY 1973; LYON, BUTLER and KEMP 1968). At present there are no data assessing the effect of centromeric heterochromatin on centromere-gene recombination. Genetics 103 797-812 April, 1983 798 1. T. EPPIG AND E. M. EICHER The second method for determining centromere-gene recombination percentages utilizes ovarian teratomas. In man and mouse these tumors originate from oocytes that have completed the first meiotic division (MI) but not the second (MII); see Figure 1 (LINDER 1969; LINDER and POWER 1970; EPPIG et al. 1977; EICHER 1978, 1981). By determining the frequency of heterozygous teratomas in heterozygous females, we can estimate recombination frequency in a manner similar to that used in Neurospora tetrad and Drosophila attached-X analyses. The ovarian teratoma mapping method has been used to estimate the recombination frequency between the centromere of human chromosome 6 and the phosphoglucomutase-3 (PGM3) locus (OTT et al. 1976a), and the centromere of mouse chromosome 7 and the glucose phosphate isomerase-1 locus (Gpi-2) (EICHER 1978). In this paper, we demonstrate that the ovarian teratoma method and the Primary Oocyte in Heterozygous Gpi-lO/Gpi-Ib Female With Crossover NO crossover Meiosis I Polor Secondary Oocyte