Intricacies of Inheritance Continued breeding experiments, better microscopes, and more scientists working in the field have advanced the knowledge of inheritance in organisms and, at the same time, complicated the simple patterns discovered by Mendel. This article covers some of the intricacies. Linkage and crossing over Shortly after the genetic community accepted Mendel's Law of Independent Assortment, several exceptions to its operation were found. Most of these exceptions were the result of linkage of the genes being studied on one chromosome. When the usual crosses were made (P 1 : parents pure-line dominant for two traits × pure-line recessive for two traits), the F 1 individuals of the cross were all dominant and presumably heterozygous. Selfing (transferring pollen from the anthers to the stigma of the same flower) of the F 1 resulted in no predictable ratios, and never the expected 9:3:3:1. Two
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