Mendelian Inheritance of RFLP "Bands on Gels"

    In diploid organisms, RFLPs and other molecular markers are typically inherited in a co-dominant mode: both alleles are physically present on the two homologous chromosomes a molecular phenotype. The phenotypes are recognized as sets of bands of particular size in electrophoresis gels. Homozygotes will show one or the other banding phenotype. In heterozygotes for two allelic RFLP patterns on alternative chromosomes, the phenotype includes the patterns from both chromosomes. In the example, the alternative homozygous phenotypes are a single band of 10Kbp in an BB individual, or two bands of 7 & 3 Kbp in an AA individual. The AB heterozygote shows both patterns, and thus has three bands of 10, 7, and 3 Kbp.

    Molecular genotypes may be detected by a variety of methods. In the electrophoresis gel shown here (top left), the bands are DNA stained with the molecular dye 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.