Читать книгу Principles of Plant Genetics and Breeding - George Acquaah - Страница 255

Mendel worked with traits that exhibited complete dominance. Post‐Mendelian studies revealed that frequently, the masking of one trait by another is only partial (called incomplete dominance or partial dominance). A cross between a red‐flowered (RR) and white‐flowered (rr) snapdragon produces pink‐flowered plants (Rr). The genotypic ratio remains 1 : 2 : 1, but a lack of complete dominance also makes the phenotypic ratio 1 : 2 : 1 (instead of the 3 : 1 expected for complete dominance).

Another situation in which there is no dominance occurs when both alleles of a heterozygote are expressed to equal degrees. The two alleles code for two equally functional and detectable gene products. Commonly observed and useful examples to plant breeding technology are allozymes, the production of different forms of the same enzyme by different alleles at the same locus. Allozymes catalyze the same reaction. This pattern of inheritance is called codominant inheritance and the gene action codominance. Some molecular markers are codominant. Whereas incomplete dominance produces blended phenotype, codominance produces distinct and separate phenotypes.