Summary

It is shown that comparison of the size of the Y chromosome between individuals may be made as reliably by computation of measurement relative to the X chromosome as by proportionation relative to the genome in the cell. By either method agreement was found with previous studies: first in placing the Y in the size range, for the cattle karyotype, between autosomes 22 and 26; second by finding the Y in the Charolais breed to be larger than other breeds. The value of the C-band method for recognition of the Y in Bos indicus, in particular, is reaffirmed and acridine orange is used to confirm the hypothesis of pericentric inversion as the basis of the relationship between the Y of Bos indicus and that of Bos taurus. The G-band pattern showed seven discernable regions in either species, so that the terminal part of the q arm in Bos indicus is homologous with the p arm in Bos taurus. The overall size and centromeric index of the Y are defined for each of 18 breeds of Bos taurus and 8 breeds of Bos indicus. It was found that the Y might be expected to be distinctive in certain breeds or groups: Afrikander, Augus, Claarolais, Friesian, Guern.rey, Hereford, Jersey, Murray Gre