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Fig. 5.28 Bipolar anaphase spindle in a monospermic ovum with chromosomes (blue) at either
pole, which will divide into two cells (left). Tripolar anaphase spindle in a dispermic ovum with
chromosomes at each pole, which will cleave into three cells (right). Mitochondria (green) are
excluded from the spindle zone. Computer colored x10,000, x8,000 (Sathananthan and Edwards
1995
; Sathananthan et al.
1999
)
abnormal increase of centrosomes. Our research on human dispermic fertilization
clearly shows three pronuclei (two male and one female) and the formation of two
sperm asters and tripolar spindles (Fig.
5.28
) and often bipolar spindles, as well
(Sathananthan and Edwards
1995
; Sathananthan et al.
1999
). Boveri's and recent
work on fruit flies (Boveri
1914
; Salisbury
2005
; Basto et al.
2008
) show that
centrosome amplification can initiate tumor formation. Many cells with extra
centrosomes initially form multipolar spindles, which later become bipolar. Cen-
trosomal amplification was also evident in human dispermic embryos (Fig.
5.21
)
which may be considered a prelude to cancer in humans? Aneuploidy is often
encountered in human IVF embryos, as well as polyploidy (Munne
2006
). This is
an important area of research that needs to be pursued. Fortunately, we do not
transfer dispermic embryos in IVF, but aneuploidy is a problem and may originate
from either sperm or egg, which is now well documented. However, IVF children
and young adults have a very slight risk of cancer according to a Reuters Health
survey, conducted by Swedish pediatricians
