Description of Quantitative Traits

Genetic and Environmental Effects

Quantitative Traits Statistics

Variance Components


Estimating Offspring Phenotype

Predicting Selection Response

Study Questions

Quantitative Genetics Overheads

Quantitative Genetics WWW Links

Genetic Topics


Finally, if you are interested in predicting the phenotype of an offspring from a cross of two parents, the portion of additive variance is important because you will know the relative contributions that the parents will make to the F1 population. Again, using our example above, if the genotype of one parent is AABB and the other parent is aabb we will know that the F1 genotype is AaBb. And if a larger portion of the genetic variance is additive then we can predict that the metric value of the F1 will be 15 bu/ac (4+2+6+3).

The general term that describes the proportion of the genetic variance to the total variance is heritability. Two specific types of heritability can be estimated. The broad-sense heritability is the ratio of total genetic variance to total phenotypic variance.

H2 = VG/VP

The narrow-sense heritability is the ratio of additive genetic variance to the total phenotypic variance.

h2 = VA/VP

Important points about heritability

  1. The heritability estimate is specific to the population and environment you are analyzing.
  2. The estimate is a population, not an individual parameter.
  3. Heritability does not indicate the degree to which a trait is genetic, it measures the proportion of the phenotypic variance that is the result of genetic factors.
Copyright © 1997. Phillip McClean