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 fourth-ranked Philadelphia housed CBS-owned WCAU-TV (channel 10) and NBC-owned WRCV-TV (channel 3, now KYW-TV), a station which NBC had acquired two years earlier through a trade with Westinghouse Broadcasting in return for NBC's television and radio stations in Cleveland. The FCC reversed the trade in 1965 and NBC regained control of the Cleveland television station, which is today known as WKYC. Each network owned stations in other markets where the other networks did not: in addition to Cleveland, these were ABC's KGO-TV (channel 7) in San Francisco and WXYZ-TV (channel 7) in Detroit, NBC's WRC-TV (channel 4) in Washington, D.C.,