You are involved in an experiment involving fluorescent painting of chromosomes. You observe the following in a nucleus experien
cing homologous pairing in metaphase I of meiosis. At appears that four chromosomes have become paired, with each chromosome pairing with two others (centromeres appear as white circles, and the four chromosomes appear in different colors). What is the best explanation of this finding
It seems that a reciprocal translocation is going on.
Explanation:
A translocation occurs when a chromosomal fragment changes its location in the same chromosome from the original to a new one. Or when it leaves the chromosome to re-locate in a new different chromosome.
According to this, there are different types of translocations:
Intrachromosomal translocations:
Intra-radial: the change in position occurs in the same arm of the chromosome. For instance, 123.456789 → 123.478569
Extra-radial: The change in position occurs from one arm to the other of the same chromosome. For instance, 123.456789 → 15623.4789
Extrachromosomal translocations:
Transposition: not reciprocal interchange. The fragment leaves a chromosome to re-locate in another chromosome. The other chromosome does not send any fragment to the first one.
Reciprocal translocation: There is a reciprocal interchange. A fragment of chromosome A goes to B, and a fragment of chromosome B goes to A.
Reciprocal translocations might be:
Fraternal: the interchange occurs among homologous chromosomes
External: the interchange occurs among non-homologous chromosomes
Reciprocal translocations are easily recognized during meiosis because an association between four chromosomes can be observed. This association is a quadrivalent structure.
During metaphase 1, the centromeres involved in the quadrivalent originate centromeric co-orientation or disjunction.
