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| Modern Genetic Analysis Chapter 14. Regulation of Gene Transcription Epigenetic Inheritance Figure 14-36. A series of crosses depicting paramutation. The B-I mutation produces pigmented plants, whereas the B mutation produces nearly unpigmented plants. Normally, when B-I is crossed with recessive colorless alleles of the b gene, the resulting plants are pigmented. However, when B-I and B plants are intercrossed, the F1 plants are essentially unpigmented, like the B homozygotes. Thus, B-I is altered by being in the same genome as B, indicated by the B-I* designation. If this outcome were due simply to the dominance of B to B-I, then a self-cross of the F1 plants should generate B-Icolored homozygotes as approximately 1/4 of the F2 progeny. Instead, no F2 are pigmented. Intercrosses of the F2 and of further generations do not restore the pigmented phenotype. Thus, B-I is said to have been paramutated by virtue of being in the same nucleus with the B allele.

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