How do multiple alleles affect inheritance patterns?

Multiple alleles can create a wider variety of phenotypes and inheritance patterns than just two alleles.

In genetics, an allele is a variant form of a gene. Most genes exist in more than two allelic forms, which is referred to as multiple alleles. This can significantly affect inheritance patterns by creating a wider variety of possible phenotypes, or observable traits.

For instance, in humans, the ABO blood group system is determined by three alleles: IA, IB, and i. IA and IB are co-dominant, meaning that when both are present, they both express their traits. The i allele is recessive to both IA and IB. This results in four possible phenotypes (blood types): A, B, AB, and O. This is a clear example of how multiple alleles can create a more complex inheritance pattern than a simple dominant-recessive relationship.

Another example is the human eye colour, which is influenced by at least three genes with multiple alleles. This results in a wide range of possible eye colours, from the most common brown to the less common green or blue, and even the very rare amber or grey.

Furthermore, multiple alleles can also lead to incomplete dominance or codominance, where neither allele is completely dominant over the other. In these cases, the heterozygous individual will express a phenotype that is a blend of the two parental traits (incomplete dominance) or will express both traits simultaneously (codominance).

In addition, multiple alleles can also influence the severity of certain genetic disorders. For example, in cystic fibrosis, different mutations in the CFTR gene can lead to varying degrees of disease severity. Some mutations cause severe symptoms, while others result in milder forms of the disease.

In conclusion, multiple alleles can greatly influence inheritance patterns by creating a wider variety of possible phenotypes, leading to incomplete dominance or codominance, and influencing the severity of genetic disorders. Understanding these patterns is crucial for predicting genetic outcomes and for diagnosing and treating genetic disorders.