Question

Define and give an example of each of the following inheritance patterns: polygenic inheritance, multifactorial trait, incomplete dominance, codominance, and multiple alleles. (pages \(479-81)\)

Short answer

Polygenic inheritance is when a trait is controlled by multiple genes, such as human skin color. A multifactorial trait is determined by genetic and environmental factors, like height in humans. Incomplete dominance results in a blend of traits, seen in pink snapdragon flowers (Rr). Codominance has both traits fully expressed, as in the AB blood type. Multiple alleles involve more than two possible alleles for a gene within a population, exemplified by the ABO blood group system.

Step-by-step solution

Polygenic Inheritance

Polygenic inheritance refers to the inheritance pattern in which a particular trait is controlled by multiple genes, each having a small effect on the overall phenotype. In other words, the genetic information for a certain characteristic is determined by more than one gene. Example: Human skin color is a classic example of a polygenic trait. It is influenced by several genes, and the various combinations of these genes determine the wide range of skin colors in humans.

Multifactorial Trait

A multifactorial trait is a characteristic that is determined by multiple genetic factors as well as environmental factors. Such traits result from the combined effect of genes and non-genetic factors. Example: Height in humans is a multifactorial trait, as it is influenced by various genes as well as environmental factors such as nutrition.

Incomplete Dominance

Incomplete dominance, also known as partial dominance, is a type of non-Mendelian inheritance pattern in which the phenotype of the heterozygous individual is intermediate between those of the two homozygous parents. Neither allele is completely dominant over the other, resulting in a blend of both traits. Example: In snapdragon flowers, there are two alleles for flower color: one for red (R) and one for white (r). When these two alleles are combined in a heterozygous individual (Rr), the flower color is pink, which is intermediate between red and white.

Codominance

Codominance refers to the inheritance pattern in which both alleles in a heterozygous individual are fully expressed, and neither is dominant over the other. As a result, the offspring display a mix of both parental phenotypes instead of a blend. Example: The AB blood type in humans is a result of codominance. When a person inherits the A allele from one parent and the B allele from the other, both alleles are fully expressed, resulting in the AB blood type.

Multiple Alleles

Multiple alleles refer to the presence of more than two possible alleles for a specific gene within a population. While any individual can only carry two alleles for a gene, there can be a larger number of alleles present in the total population. Example: The ABO blood group system in humans is an example of multiple alleles. There are three different alleles for the gene that determines blood type: A, B, and O. While any individual can only inherit two of these alleles (one from each parent), all three can be found within the population.