Mendelian Inheritance of RFLP "Bands on Gels"

    RFLPs and other molecular markers are typically inherited in a co-dominant mode: both alleles are expressed as  a molecular phenotype. The phenotypes are recognized as sets of bands of particular size in electrophoresis gels. In the case of an individual heterozygous for two allelic RFLP patterns on alternative chromosomes, the phenotype includes the patterns from both chromosomes. In the example, the alternative alleles patterns are a single band of 10Kb, or two bands of 7 & 3 Kb. The heterozygote shows both patterns, and thus has three bands of 10, 7, and 3 Kb.

    Molecular genotypes may be detected by a variety of methods. In electrophoresis gels (top left), the bands are DNA stained with ethidium bromide that fluoresces under ultraviolet light, so that they appear as red-orange bands against a black background.  In Southern blots (bottom left), the bands are DNA probed with radioactive labels that cause the DNA to expose X-ray film, so that they appear as dark bands against a gray background.