Human and swine chromosomes were analyzed separately and as a mix to obtain bivariate flow karyotypes. They were normalized to each other in order to use the human chromosomal DNA content as standard. Our results led to the characterization of the "DNA line" in swine identical to the human "DNA line." Estimation of the DNA content in megabase pairs of the swine chromosomes is proposed. Chromosomal assignment to the various resolved peaks on the bivariate swine flow karyotype is suggested from the relation between DNA content quantified by flow cytometry and chromosomal size. Swine chromosomes 1,13, 6,5,10,16,11,18, and Y were assigned to peaks A, B, C, K, L, N, 0, Q, and Y, respectively. Peaks D and E were assumed to contain chromosomes 2 and 14, but without specific assignment. Similarly, P and M peaks were expected to correspond to chromosomes 12 and 17. Of the remaining chromosomes (3, 7, X, 8, 15, 9, and 4), chromosomes 3, 7, and X, which were assigned previously to peaks F, G, and H, respectively, led us to deduce that chromosomes 15 and 8 belonged to peaks I and J, and chromosomes 9,4, and X to peak H. CI 1992 Wiley-Liss, Inc.Key terms: DNA line, chromosome identification Flow cytogenetic techniques already contribute greatly to our knowledge of the genome in mammals. They have, for instance, proved invaluable in detecting numeral and structural aberrations associated with human genetic diseases. They have also been extensively applied to human chromosome sorting, thereby permitting the construction of chromosome-specific DNA libraries (see ref. 6 for review). Applied to domestic species, flow cytometric techniques have been particularly straightforward in swine cytogenetic analyses, as most of the chromosomes in this species are both fairly different in size, and are fewer in number compared with human or bovine chromosomes (22).Flow cytogenetics and chromosome sorting therefore appear especially relevant for the ongoing European PiGMaP project (2). Among the aims of the project is the construction of chromosome-specific libraries, in order to provide as quickly as possible chromosome-assigned markers, which in conjunction with other techniques will allow coverage of the whole genome. A prerequisite to production of chromosome-specific libraries is accurate assignment of all, or at least most, of the swine chromosomes to the peaks of the flow karyotype and the estimation of the swine chromosomal DNA content. We therefore further developed studies on bivariate flow karyotypes in swine, as previous results showed that good chromosome resolution was easily achievable (7,s). All swine chromosome types could be resolved into individual peaks except two autosomal pairs plus chromosome X, which were confounded (15).The work reported here concerns the establishment of a "DNA line" in swine, a technique successfully applied to human chromosomes (17,3,18 somes to the various peaks on the bivariate flow karyotype. MATERIALS AND METHODSAnimals We analyzed the karyotypes of 11 pigs of both sexes, 9 males and 2 females...

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