Final answer:
Most traits are controlled by multiple genes, but some traits are controlled by a single gene. These single-gene traits follow Mendelian inheritance patterns. However, it's important to note that single observable characteristics are almost always influenced by multiple genes working together. The control of traits and inheritance is complex and involves a combination of multiple genes and alleles.
Step-by-step explanation:
Most traits are controlled by multiple genes, but some traits are controlled by a single gene. These single-gene traits are called Mendelian traits and are inherited according to Mendelian inheritance patterns. In Mendelian inheritance, there are two alleles, one of which may be dominant to the other. For example, cleft chin is a dominant trait controlled by a single gene. If an individual has at least one copy of the dominant allele, they will have a cleft chin phenotype.
However, it's important to note that single observable characteristics are almost always under the influence of multiple genes, each with two or more alleles acting together. For example, color in humans is influenced by at least eight genes. So while single-gene traits exist, they are not the most common controlling factor for traits and inheritance.
Overall, the control of traits and inheritance is complex and involves a combination of multiple genes and alleles.