Complex Patterns

By: raymone fuller

Multiple alleles

a series of three or more alternative or alleles forms of a gene, only two of which can exist in any normal, diploid individual.

Examples: Two human examples of multiple-allele genes are the gene of the ABO blood group system, and the human-leukocyte-associated antigen genes. The ABO system in humans is controlled by three alleles, usually referred to as IA, IB, and IO (the "I" stands for isohaemagglutinin).

Incomplete dominance


    Incomplete dominance refers to a genetic situation in which one allele does not completely dominate another allele, and therefore results in a new phenotype.

    Example1:

    A snapdragon flower that is pink as a result of cross-pollination between a red flower and a white flower when neither the white or the red alleles are dominant.
    Example2:
    A brown fur coat on a rabbit as a result of one rabbit's red allele and one rabbit's white allele not dominating.


Codominance

Codominance is a relationship between two versions of a gene. Individuals receive one version of a gene, called an allele, from each parent. If the alleles are different, the dominant allele usually will be expressed, while the effect of the other allele, called recessive, is masked.

Example1: Examples of codominance include a person with type AB blood, which means that both the A allele and the B allele are equally expressed

Example2: If a black cat and tan cat mate, the kitten will have both black fur and tan fur.

If a dog with white fur and a dog with black fur mate, they produce a dog with both white and black fur.

Polygenic traits

A polygenic trait is one whose phenotype is influenced by more than one gene. Traits that display a continuous distribution, such as height or skin color, are polygenic.

Example1:

Humans can be many different sizes. Height is a polygenic trait, controlled by at least three genes with six alleles. If you are dominant for all of the alleles for height, then you will be very tall. There is also a wide range of skin color across people.