Patterns in Inheritance

Non-Mendelian Traits Overview

Non-Mendelian traits are genetic traits that do not follow the typical Mendelian inheritance patterns.
Unlike Mendelian traits that have clear dominant and recessive alleles, non-Mendelian traits may exhibit more complex inheritance patterns.

Incomplete dominance occurs when the dominant allele is not completely expressed in the presence of a recessive allele.
Example: Snapdragons can have three phenotypes: red (RR), white (rr), and pink (Rr). Pink flowers result from the mixing of red and white traits.
Punnett Square for Pink Flowe:
- Crossing two pink snapdragons (Rr x Rr) can produce red, white, and pink offspring.

Codominance occurs when both alleles in a heterozygote are fully expressed, resulting in offspring that exhibit both traits simultaneously.
Example: In speckled chickens, crossing a black chicken (BB) with a white chicken (WW) produces offspring that are both black and white (BW).
The different letters for alleles (B and W) indicate that both traits show equally in the phenotype.

Traits like human height and skin color are influenced by multiple genes, resulting in a continuous range of phenotypes.
There is no single pair of alleles determining these traits; instead, multiple genes contribute to the overall phenotype (e.g., AABbCcDD).
Environmental factors (e.g., nutrition, sunlight) can also influence these traits without altering the underlying genetics.

Epistasis occurs when the expression of one gene is dependent on the presence of another gene.
Example: In llamas, a dominant B allele (black wool) can be masked by an epistatic gene (C) that determines if pigment can be expressed.
The recessive genotype (cc) will prevent wool color from being expressed, resulting in an albino llama, regardless of the B allele present.
To study epistasis, dihybrid crosses (e.g., BbCc x BbCc) are used, demonstrating that the phenotype can depend on the interaction between two genes.

Non-Mendelian genetics reveal complexities in inheritance that provide a broader understanding of how traits are passed on.
When solving genetics problems, always look for clues indicating whether a trait is non-Mendelian.