Linked alleles, for example, -band aB,
form the gametes -band a-B that
maintain the of the alleles. This
of linkage is called
linkage. Inthe first division meiosis
(meiosisI) however the over
phenomenon may occur.
from a pair of may
exchange extremities and once
linked alleles, for , A-band a-B,
recombine to different gametes, in
the , A-B and a-b.

Crossing may happen when the
of the chromatids of
homologous are paired during .
Matching portions of the of
two nonsister chromatids ( from one
homologous of pair) break and the
are exchanged, each of
becoming part of the of the other
chromatid. example, if the allele is
situated in a of the arm relating
the point of breaking the allele b is
in the other side, will be
separated and A-B and a-b will
formed, instead of A-band -B.
(The percentage of recombinant
relating to normal gametes
upon the crossing over
that in itsturn depends how far
distant the alleles are in the
.)