Final answer:
Most traits do not adhere to simple Mendelian genetics because of factors such as incomplete dominance, codominance, multiple alleles, and polygenic traits, all of which produce a more complex pattern of inheritance.
Step-by-step explanation:
Complex Patterns of Inheritance
Most traits do not follow simple Mendelian inheritance of dominant and recessive traits. This is due to phenomena such as incomplete dominance, codominance, multiple alleles, and polygenic traits. In incomplete dominance, the resulting phenotype is intermediate between both parents, as seen with the pink flowers from red and white snapdragons. With codominance, both alleles are fully expressed, such as human blood types AB. Multiple alleles mean that more than two alleles exist for a gene, increasing the diversity of possible phenotypes. Lastly, polygenic traits involve multiple genes contributing to a single characteristic, such as height or skin color, and are typically influenced by environmental factors as well.
Non-Mendelian inheritance patterns explain why the principle of dominance does not always apply. For example, two parents with a dominant phenotype may have offspring with a recessive phenotype if both parents are heterozygous. Moreover, traits thought to be recessive can exhibit mild forms or biochemical abnormalities when one recessive allele is present, suggesting a blending of traits.