compare inheritance by multiple alleles and polygenic inheritance

To compare inheritance by multiple alleles and polygenic inheritance, we need to understand the basic concepts behind each type of inheritance.

1. Inheritance by multiple alleles:
This type of inheritance occurs when a gene has more than two alternative forms, known as alleles. These alleles can be found on the same gene locus on the chromosomes. However, an individual can only inherit two alleles for a particular gene, one from each parent.

Example: The ABO blood group system in humans is a classic example of inheritance by multiple alleles. The gene responsible for determining blood type has three alleles: A, B, and O. A person can have blood group A (IAIA or IAi), B (IBIB or IBi), AB (IAIB), or O (ii), depending on the combination of alleles inherited.

2. Polygenic inheritance:
Polygenic inheritance occurs when a trait is controlled by the actions of multiple genes, each with various alleles. These genes are usually non-linked and located on different chromosomes. The phenotype of a polygenic trait is influenced by the additive effects of each allele.

Example: Human height is a polygenic trait. It is influenced by the combined effects of multiple genes, each with different alleles. The more "tall" alleles an individual inherits, the taller they are likely to be. Conversely, the more "short" alleles they inherit, the shorter they are likely to be.

Now, let's compare these two types of inheritance:

1. Number of genes and alleles:
Inheritance by multiple alleles involves a single gene with more than two alleles. Polygenic inheritance involves multiple genes, each with multiple alleles.

2. Genetic variation:
Inheritance by multiple alleles contributes to genetic variation by providing different possible combinations of alleles for a single gene. Polygenic inheritance, on the other hand, contributes to genetic variation by the cumulative effects of multiple genes.

3. Phenotypic variation:
Inheritance by multiple alleles results in discrete phenotypes, as each allele combination produces a distinct trait. Polygenic inheritance leads to continuous phenotypic variation, where the trait can range along a spectrum.

4. Environmental influence:
Inheritance by multiple alleles is less influenced by environmental factors, as the phenotype is primarily determined by the specific combination of alleles inherited. Polygenic inheritance is significantly influenced by environmental factors, which can affect gene expression and ultimately impact the phenotype.

In summary, inheritance by multiple alleles involves a single gene with more than two alleles, resulting in discrete phenotypes. Polygenic inheritance, on the other hand, involves multiple genes with multiple alleles, leading to continuous phenotypic variation influenced by both genes and the environment.