The phenotype observed is part of a distinct class example: yellow vs. green. Single genes controlled by Mendellian principles.
Controlled by more than one gene each one individually follows Mendellian Principles: Polygenic.
When polygens interact with diverse environmental factors
Additive Model of Polygenic/Multifactorial Trait Inheritance
1. Quantified by the degree of the characteristic expressed by an individual
2. Wide Phenotypic variation and is analyzed in populations individuals3. Controled by at least 2 genes
4. Individuals genes inheritted in a Mendallian fashion.
5. The effect of each allele is relatively small
6. Strong allele makes an equal contribution and weak allele makes no contribution
7. Polygens will give rise to classes of phenotypes depending upon the number of genes contributing to the trait.
8. Internal and External environment will put classes into a bell shaped curve of phenotypes.
1. Presence of different genotypes in members of the population
2. The presence of different environments in which all the genotypes have been expressed
Proportion of the total phenotypic variance caused by genetic differences. High if it is due to genetic variance low if it is not closer to one the higher it is.
Limits on Heritability
1. Not possible to obtain an absolute heritability for any trait
2. characteristic of the population and does not apply to individuals
3. The two study groups will differ in genotypes and environment exposure in unkown ways
Family Relatedness Method
The study of multiple family groups where the degree of relatedness is known. Heritability= Observed Correlation/ Expected Correlation
Identical Twins have the same genotype any variatuion in phenotype must be due to the environment. Faternal twins can differ in both genotype and environment, the difference should lie in the genotype. Adopted children raised in same environment.
Disease related genotype freequencies in the population are distributed along the expected bell-shaped curve. Individuals above a gentic threshold will develop the disorder, if and when they are exposed to certain environmental conditions.
Trait controlled by multiple genes. ridge counts are useful for study of phenotypic variance and heritability.
Multifactorial trait. Controlled by genotype and the environment
Multifactorial Trait. Also controlled by gentics but is sex linked as well.
Multifactorial type with sufficient environmental contribution.
10 genes are involved in controlling blood presser (hypertension). Environment (fatty diet, salty diet, alcohol intake, stress and insufficient exercise) also contributes
Mental Conditions and Abilites
Difficult to label specif genetic correlation, but the environment does play a part