Quantitative variation of LINE-1 sequences in five species and three subspecies of the subgenus Mus and in five Robertsonian races of Mus musculus domesticus.

The quantitative variation of a conserved
region of the LINE-1 ORF2 sequence was determined
in eight species and subspecies of the subgenus Mus
(M. m. domesticus, M. m. musculus, M. m. castaneus,
M. spicilegus, M. spretus, M. cervicolor, M. cookii, M.
caroli) and five Robertsonian races of M. m. domesticus.
No differences in LINE-1 ORF2 content were
found between all acrocentric or Robertsonian chromosome
races, whereas the quantitative variation of
the LINE-1 ORF2 sequences detected among the
eight taxa partly matches with the clades into which
the subgenus is divided. An accumulation of LINE-1ORF2 elements likely occurred during the evolution
of the subgenus. Within the Asiatic clade, M. cervicolor,
cookii, and caroli show a low quantity of
LINE-1 sequences, also detected within the Palearctic
clade in M. m. castaneus and M. spretus, representing
perhaps the ancestral condition within the subgenus.
On the other hand, M. m. domesticus, M. m. musculus
and M. spicilegus showed a high content of LINE-1
ORF2 sequences. Comparison between the chromosomal
hybridization pattern of M. m. domesticus,
which possesses the highest content, and M. spicilegus
did not show any difference in the LINE-1 ORF2 distribution, suggesting that the quantitative variation
of this sequence family did not involve chromosome
restructuring or a preferential chromosome accumulation,
during the evolution of M. m. domesticus.