5. Non Mendel Inheritance

Non-Mendelian Inheritance

Inheritance patterns involving genetic mechanisms or interactions that do not follow simple Mendelian patterns, often involving multiple genes, allele interactions, or environmental influences.

Incomplete Dominance

An inheritance pattern in which a heterozygote has an intermediate phenotype between the two homozygous phenotypes.

Incomplete Dominance Example

In snapdragons, crossing a red-flowered plant with a white-flowered plant produces pink-flowered offspring.

Codominance

An inheritance pattern in which both alleles are fully and simultaneously expressed in a heterozygote.

Codominance Example

In the ABO blood group system, individuals with AB blood type express both A and B antigens.

Multiple Alleles

A pattern in which more than two alleles for a gene exist in a population, although an individual can carry only two alleles at a specific locus.

Multiple Alleles Example

The human ABO blood group system has three alleles: Iᴬ, Iᴮ, and i.

Epistasis

A gene interaction in which alleles of one gene mask or modify the expression of alleles at another gene.

Epistasis Effect

Epistasis can alter the phenotypic ratio expected from independent action of individual genes.

Epistasis Example

In Labrador Retrievers, one gene controls pigment production while another controls pigment deposition, affecting coat color.

Polygenic Inheritance

An inheritance pattern in which multiple genes contribute to a single trait, producing a continuous range of phenotypic variation.

Polygenic Trait

A trait influenced by multiple genes that typically shows continuous variation among individuals.

Polygenic Inheritance Examples

Human height and skin color are examples of traits influenced by multiple genes.

Incomplete Dominance vs Codominance

In incomplete dominance, the heterozygote shows an intermediate phenotype; in codominance, both alleles are fully expressed.

Multiple Alleles vs Codominance

Multiple alleles means more than two alleles exist in the population; codominance means both alleles are simultaneously expressed in a heterozygote.

Epistasis vs Polygenic Inheritance

Epistasis involves one gene masking or modifying another gene; polygenic inheritance involves multiple genes contributing to one trait.

Major Non-Mendelian Patterns

Incomplete dominance, codominance, multiple alleles, epistasis, and polygenic inheritance.