Heterosexual chimerism among singleton females produced by multiple no
nsexed embryo transfer (MNET singleton females) was investigated using
chromosome typing and PCR (polymerase chain reaction)-amplification o
f male-specific DNA (msDNA). Of the 22 animals tested, 21 were classif
ied as normal by both methods (i.e., showing no male cells among 100 m
etaphase spreads in chromosome typing and being msDNA negative in PCR)
. No morphological abnormalities of the genital organs were observed a
mong 19 MNET single females. One MNET singleton female was, however,cl
assified as a freemartin by PCR (male-specific DNA positive), but it w
as classified as normal cytogenetically. This individual probably had
a low degree of heterosexual chimerism, and it seems that the chimeris
m derived from MNET was difficult to diagnose by chromosome typing, al
though it was detectable by PCR. The genital organs of this individual
(15-mo-old Aberdeen Angus) were normal in form (both external and int
ernal) and size. However, a very small structure, resembling seminifer
ous tubule, was found in the left ovary. It may be concluded that most
MNET singleton females are expected to have normal reproductive funct
ion.