From Wikipedia,
the free encyclopedia.
A chromatid forms one
part of a
chromosome after it has
coalesced for the process of
mitosis or
meiosis. During either
process, the word "chromosome"
indicates a pair of two exactly
identical ("sister")
chromatids joined at the central
point of each chromatid, called
the
centromere.
A chromosome, by definition,
has exactly one centromere. Thus
when sister chromatids are pulled
apart by the
mitotic spindle during
anaphase -- that is, when the
centromere joining two sister
chromatids splits into two
centromeres -- then each sister
chromatid becomes an independent
chromosome.
In non-gametic, non-dividing
human cells, there are 23 pairs of
chromosomes, thus 46 chromosomes.
When it is ready to divide, each
chromosome will replicate itself
during the Synthesis phase within
its life cycle, making a total of
92 chromatids (remember, since the
term "chromosome" is redefined,
the number of chromosomes remains
46 despite the replication).
