Polygenic and Complex traits

Monogenic

1 gene leads to two discrete phenotypes dominant (Aa or AA) and recessive (aa.)

Polygenic trait

Many genes lead to phenotypes.

Multifactorial trait

Genetics AND environment lead to phenotype

What are discrete traits?

Distinct and limited categories of phenotypes with no intermediates and any differences are due to variation in a single gene.

What are quantitative traits?

No distinct categories of phenotypes, so we can have a continuous range of phenotypes. Any differences are due to a variation in multiple genes and the environment.

Quantitative Trait Loci (QTLs)

Region in a genome that correlates with variation of phenotypes for a quantitative trait in a population of organisms

Continuous Trait

Any value between two extremes, continuous bell curve. Many phenotypes and they can fall within a range.

Meristic trait

Any whole number between two extremes 1 baby, 2 baby, 3 baby. Other way to say it is that we can have many phenotypes, but we can only be 1.

Threshold trait

Binary phenotype determined by continuously varying susceptibility

• there is a threshold for susceptibility for a disease; likely will get disease or DO HAVE disease

Additive alleles

Equal effects, unlinked, no environmental effects ??

1/4^n gives us what?

Individuals that are homozygous for a recessive or dominant trait given any number of genes for that trait (n)

2n+1 gives us what?

How many possible phenotypes considering number of polygenic genes(n)

• This formula assumes each gene has 2 alleles (one dominant, one recessive)

• The "n" represents the number of genes involved in the trait

• Each gene contributes additively to the phenotype

Phenotype variation

Vp=Vg+Ve+(Vg*E)

Heritability

Heritability H²=Vg/Vp

Larger heritability value means

Narrow scope of phenotype, more explained by genetics

Smaller heritability value means

Broader scope of phenotypes, less explained by genetics