Non Mendel

Incomplete Dominance

An inheritance pattern in which the heterozygous offspring displays an intermediate phenotype between the two homozygous parents.

Incomplete Dominance Example

Red flowers (RR) crossed with white flowers (WW) produce pink flowers (RW).

Incomplete Dominance Genotypes

RR = red; RW = pink; WW = white.

Incomplete Dominance F1 Generation

The first-generation offspring show an intermediate phenotype between the two parental phenotypes.

Incomplete Dominance vs. Complete Dominance

In incomplete dominance, the heterozygote has an intermediate phenotype; in complete dominance, the heterozygote expresses the dominant phenotype.

Incomplete Dominance F2 Phenotypic Ratio

When two heterozygous individuals are crossed, the typical phenotypic ratio is 1 red : 2 pink : 1 white.

Codominance

An inheritance pattern in which both alleles are fully expressed in the heterozygote, producing separate, distinguishable traits.

Codominance Example

AB blood type, in which both A and B antigens are expressed on red blood cells.

Codominance Genotypes (ABO Blood Group)

IᴬIᴮ = AB blood type; both A and B antigens are expressed.

Codominance in Cattle

A red-haired cow crossed with a white-haired cow can produce roan offspring with both red and white hairs.

Codominance vs. Incomplete Dominance

Codominance expresses both parental traits distinctly; incomplete dominance produces an intermediate phenotype.

Epistasis

A genetic phenomenon in which one gene affects or masks the expression of another gene.

Epistatic Gene

The gene that masks or modifies the expression of another gene.

Hypostatic Gene

The gene whose expression is masked or modified by another gene.

Epistasis Example in Labrador Retrievers

The E gene controls pigment deposition in fur; the ee genotype produces yellow fur regardless of the B gene's genotype.

Epistasis vs. Dominance

Dominance occurs between alleles of the same gene; epistasis occurs between different genes.

Pleiotropy

A genetic phenomenon in which a single gene or genetic variant affects multiple phenotypic traits.

Pleiotropic Gene

A gene that influences multiple traits or characteristics in an organism.

Pleiotropy Example: Marfan Syndrome

A mutation in the FBN1 gene affects multiple body systems, including the skeleton, eyes, and cardiovascular system.

Pleiotropy Example: Sickle Cell Disease

A mutation in the HBB gene affects red blood cells and can also affect multiple organs and body systems.

Pleiotropy vs. Epistasis

Pleiotropy occurs when one gene affects multiple traits; epistasis occurs when one gene affects or masks the expression of another gene.

Polygenic Inheritance

An inheritance pattern in which multiple genes contribute to a single trait, each often having a small additive effect on the phenotype.

Polygenic Trait

A trait influenced by multiple genes, often showing continuous variation.

Polygenic Inheritance Examples

Human height, skin color, and eye color.

Polygenic Inheritance and Variation

Multiple genes contribute to a wide range of phenotypes rather than a few distinct categories.

Polygenic Inheritance vs. Pleiotropy

Polygenic inheritance occurs when multiple genes influence one trait; pleiotropy occurs when one gene influences multiple traits.

Polygenic Inheritance vs. Mendelian Inheritance

Polygenic traits are influenced by multiple genes and often show continuous variation; simple Mendelian traits are typically controlled by one gene.

Multifactorial Inheritance

A pattern in which traits or diseases result from the combined effects of multiple genes and environmental factors.

Multifactorial Trait

A trait influenced by multiple genes and environmental conditions, such as diet, lifestyle, and environmental exposure.

Multifactorial Inheritance: Genetic Factors

Multiple genes contribute to the development of a trait or disease.

Multifactorial Inheritance: Environmental Factors

Factors such as diet, lifestyle, and environmental exposure can influence the expression or risk of a trait or disease.

Multifactorial Inheritance Examples

Heart disease, type 2 diabetes, Alzheimer's disease, cleft lip, and schizophrenia.

Multifactorial Inheritance: Family Risk

These conditions can run in families, and closer relatives of an affected person may have an increased risk.

Multifactorial Inheritance: Predictability

Risk is complex and does not follow a simple, predictable Mendelian inheritance pattern.

Polygenic vs. Multifactorial Inheritance

Polygenic inheritance involves multiple genes affecting a trait; multifactorial inheritance involves multiple genes and environmental influences.