Evidence of Age Aneuploidy in the Chromosomes of the Sheep

Abstract

VARIATIONS in chromosome counts associated with age were first shown in human leucocyte cultures by Jacobs et al.¹. I have examined the chromosomes of twenty-two normal ewes and rams and six freemartin sheep in preparations made by a method similar to that of Basrur and Gilman², and have counted chromosomes in at least fifty metaphases in each case. Several cultures were prepared from each freemartin and were then counted to see if there was a relationship between XY cells and the degree of masculinization as reported before^3,4; these results are reported elsewhere⁵. In none of the twenty-two normal sheep was any chromosome abnormality observed; in the freemartin sheep, however, there was XX and XY white blood cell chimaerism. The chromosome counts of the six freemartin sheep are recorded in Table 1 and the percentage of hypomodal and hypermodal modal cells in each of these are given in Table 2.