'Fossil' DNA sequences found only in the S subgenome (chromosomes) of
Xenopus laevis emit a red glow employing the FISH method. The nine S
chromosomes here clearly possess a larger number of red regions, believed to
have derived from ancestral species S. (Chromosome 9, at bottom right, is
represented as '9_10,' as it corresponds to the fusion of ancestral
chromosomes corresponding to chromosomes 9 and 10 in Xenopus tropicalis).