Molecular Biology and Evolution, Vol 9, 331-365, Copyright © 1992 by Society for Molecular Biology and Evolution
FS Nallaseth
When the Y chromosome from Mus. poschiavinus (YPos) is backcrossed onto the
C57BL/6J laboratory strain, testicular dysfunction occurs at high
frequencies. When five different multicopy probes from the
recombinationally suppressed region of the Y chromosome were used, genomic
DNAs from sibling female progeny of C57BL/6J YPos males were found to
contain YPos-specific sequences ranging from trace levels to levels
consistent with an intact Y chromosome. Females with a high copy number of
YPos-specific sequences had a karyotype of XYPos and were sterile. Females
with trace levels of these sequences were XX and fertile. Repeated
sequences in the testis-determining-region (Sxr) of inactive YPos
chromosomes were unstable relative to sequences in non- Sxr regions. In
contrast, the YPos chromosome was stable and functioned normally in other
inbred laboratory strains such as 129/Sv. The frequency and extent of YPos
chromosome instability increased with successive backcrosses from stable
(129/Sv) to unstable (C57BL/6J) genetic backgrounds. Traces of
YPos-specific sequences were first detected in N2 female offspring of F1
males. Therefore, sequences were deleted from YPos chromosomes in the F1
male germ line and were transmitted to N2 females; inactive YPos
chromosomes (XYPos females) were first detected in the N3 generation. The
mouse line being derived by backcrossing the YPos chromosome onto C57BL/6J
inbred strains ended in the N7 generation, since all XYPos offspring were
sterile. Even stable repeated sequences from the non-Sxr regions of their
inactive YPos chromosomes were precisely rearranged in these N7 offspring
at high frequencies. These data are consistent with hybrid dysgenesis in
mammals.
ORIGINAL ARTICLE
Sequence instability and functional inactivation of murine Y chromosomes can occur on a specific genetic background
Department of Cell and Developmental Biology, Roche Research Center 94720.
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