Deoxyribonucleic acid content of marsupial nuclei.

Abstract

THE deoxyribonucleic acid content of nuclei of different species of animals has been listed1; there appears to be a fairly regular increase from the sponges to the mammals. In the sponges the amount is about 0.1 × 10−12 gm. per diploid nucleus, in mammals it is about 6.0 × 10−12 gm. In birds the amount is only a little more than a third of that found in mammals, being about 2.3 × 10−12 gm. As pointed out by White2, there is a distinct break in the distribution of chromosome numbers of the mammals, the Eutherian mammals with few exceptions having a haploid number of the order of 20–30, the marsupials of the order of 6–12. The birds and monotremes both have considerably larger numbers, and resemble the reptiles in this respect. There are, then, at least two major characters by which the higher vertebrates differ: first, the deoxyribonucleic acid content of the nucleus, and secondly, the number of chromosomes. The two do not necessarily parallel one another; but there seems to be a tendency for the groups with many chromosomes to have less deoxyribonucleic acid. The deoxyribonucleic acid content of marsupial nuclei has not heretofore been measured, and investigations of this group are reported here.