Epigenetic regulation of transposable elements in the plant kingdom which allows for self-copying) within the coding of the transposon defines class I elements as autonomous or non-autonomous. Class I transposons can take the form of: Curiously, retrotransposons have been discovered to be the predominant form of transpositional element in plants with large genomes, such as maize and wheat, potentially indicating rapid success of this class of transposon in the creation of hybrids, such as wheat, peppermint and, in the distant past, maize. Plant hybridization often creates polyploids, with double, triple, quadruple or more the number of chromosomes present in the parent generation. Polyploid hybrids seem to be particularly susceptible
Owned-and-operated television stations in the United States Westinghouse to trade its NBC-affiliated Philadelphia cluster of KYW-AM (1060) and WPTZ-TV (channel 3) to NBC in exchange for WTAM-AM-FM and WNBK-TV in Cleveland. Westinghouse only agreed to the trade after NBC threatened not only to yank its programming from WPTZ, but also Westinghouse-owned WBZ-TV (channel 4) in Boston. NBC changed the callsigns of the Philadelphia stations to WRCV-AM-TV, while Westinghouse changed the Cleveland stations' callsigns to KYW-AM-FM-TV. NBC's then-ownership of Philadelphia's channel 3 was cited by CBS when it purchased its then-affiliate WCAU-TV in 1958, despite FCC rules at the time barring companies from owning stations with overlapping signals,