From Wikipedia,
the free encyclopedia
- The term "Chiasma" is
also sometimes used to refer to
the
Optic chiasm.
A chiasma, related to
the Greek letter "X", is the
technical term for the point where
two
chromatids are intertwined
(interwoven) in a
cell. The chiasmata are
thought to be the points where two
nonsister chromatids exchange
genetic material during
chromosomal crossover during
meiosis(sister chromatids also
form chiasmata between each other,
but because their genetic material
is identical, it doesn't cause any
change in the resulting daughter
cells). The chiasmata become
visible during the diplonema stage
of meiosis, but the actual
"crossing-over" of genetic
material is thought to occur
during the previous pachytene
Stage. When tetrads, which are
composed of two pairs of sister
chromatids, begin to split the
only points of contact are at the
chiasmata.
Chiasma frequency = 2 x
recombination frequency
where recombination frequency
is
recombination frequency = (No.
of recombinants)/(total no. of
progeny) x 100
