Centric fusion of acrocentric chromosomes

Chromosome 14 and chromosome 21 (1) are the
most frequently involved in fusions (about 1 in
1000 newborns). By fusion of the long arm of
chromosome 21 (21q) and the long arm of chromosome
14 (14q), a chromosome t (14q21q) is
formed (2). The satellite-carrying short arms of
both chromosomes are lost, but this is insignificant.
When germ cells (gametes) are formed,
deviation from the normal chromosome number
may result (3). Since chromosome 14 and
chromosome 21 pair during meiosis, the following
possible gametes may result: chromosome
14 alone (no chromosome 21), one chromosome
14 and one chromosome 21 (normal),
the chromosome 14 fused to chromosome 21
(balanced), or the fused chromosome and one
chromosome 21