These mice express a mini-gene construct that contains the 5'- and 3'-ends of the human gene for the pro-alpha(1) collagen chain but lack a large central region containing 41 exons. The mini-gene includes 2.5 kilobases of the 5'-promoter region, the first 5 exons and introns, the last 6 exons and introns, and about 2 kilobases of the 3"flanking region. The junction between the 5'- and 3'-halves of the mini-gene was made in introns so as to preserve the consensus sequences for RNA splicing. Mice in this line carry about 20 copies of the transgene.