Chronology of DNA replication in the sex chromosomes of the reindeer (<i>Rangifer tarandus</i> L.)

Abstract

The chromosomes of the reindeer (2n = 70) were studied with special reference to the chronology of DNA replication of the sex chromosomes. The X chromosome was metacentric and nearly of the duplicate type, being about 9% in length of the total complement. All the other chromosomes, including the Y, were acrocentric except one submetacentric pair. The X and Y chromosomes were apparently terminally associated at first meiotic metaphase in the male. A single, rather large chromocenter was observed in the majority of cultured female cells. The male cells were predominately negative but occasionally demonstrated a somewhat smaller, distinct chromocenter. Autoradiography showed that in the female cultured cells the ‘one entire X plus half of the other X heavily labelled’ pattern was conspicuously present at the end of the S period. A quantitative analysis indicated that one hour from the end of the S period both X chromosomes were uniformely labelled. One X was still completely labelled, while one arm of the other was not 45 min before the end of S, and at 30 min only one arm in each X chromosome was labelled. The two X chromosomes then seemed to be slightly asynchronous until the very end of S. In the male cells semiquantitative analysis indicated that one arm of the X and the entire Y chromosome were synchronous in terminating DNA synthesis.

DNA synthesis in duplicate-type sex chromosomes of the Indian house shrew, <i>Suncus murinus</i> (Insectivora)

“…This extra translocated heterochromatin has been shown to replicate late in the S phase. Thus duplicate-and triplicate-type X chromosomes replicate late in all but one half and one third, respectively, of their length (corresponding to the originaltype X) in the sitatunga and blackbuck (Wurster et al, 1968) and in reindeer (Fraccaro et al, 1968). In Sunctts, on the contrary, the entire duplicate-type X and large Y show out-of-phase replication, the duplicate-type X in females showing early or late replication, the large Y in males only early replication.…”

Comparative FISH mapping of bovine cosmids to reindeer chromosomes demonstrates conservation of the X-chromosome

“…The short arm of reindeer and the long arm of cattle X chromosomes represent approximately the same fraction of their respective haploid genomes (3.61% and 3.43% respectively, Fraccaro et al 1968, Popescu 1969, Lin et al 1977. The linear order and locations (middle and terminal) of the two cosmids (cIOBT 945 and 1489) on the respective arms of the X chromosome of the two species is also strikingly similar ( Figure 1B), suggesting correspondence at the chromosome structure and DNA levels.…”

“…Karyotypically, these represent two very divergent species. The chromosome number in reindeer is 2n = 70 (number of major chromosome arms, nombre fondamental, nf = 74 according to Matthey 1945), comprising 33 pairs of acrocentric autosomes, one pair of submetacentric autosomes and a pair of sex chromosomes (Nes et al 1965, Fraccaro et al 1968, Gripenberg 1984. On the other hand, cattle have 2n = 60 (nf= 62) and all 29 pairs of autosomes are acrocentric.…”

“…However, the giant size of the X chromosome of reindeer has been of special interest, ever since the chromosomes of this species were first known (Makino 1944). This chromosome is remarkably long, comprising about 9% of the haploid female genome (Fraccaro et al 1968), compared with about 5-6% in cattle and in most other mammalian species (Ohno et al 1964). Therefore, the reindeer X chromosome is considered as a representative of a specific type of mammalian X (with almost double the typical contribution to the haploid genome), similar to the X chromosome observed in some rodent species (Ohno et al 1964).…”

A fragile site in the X chromosome of the reindeer (Rangifer tarandus L)

“…Figure 1 shows the G-and subsequently C-banded chromosomes of the reindeer (Gripenberg, 1984). The X chromosome is of 'the duplicate type' or comprises 9% of the total complement, while the mammalian X usually comprises 5% of the genome (Fraccaro et al, 1968).…”