Heritability

1. An assignment on Heritability
Date of Submission: 2080/01/24
Submitted by: Rabins Subedi Submitted to : Surya Dhungana
Department Plant Breeding and Genetics Assistant Professor
AFU AFU

2. HERITABILITY
Proportion of the total phenotypic variation that is due to genotypic variation
among individuals for a particular trait.
 It is the proportion of the observed variation in a progeny that is inherited.
Simply, it is the ratio of genetically caused variation to total variation.
Always measured in a population in a particular trait.

3. Types of heritability
 2 types
a. Broad sense heritability
b. Narrow sense heritability

4. a. Broad sense heritability
Proportion of phenotypic variance that is due to total genetic variance (additive,
dominance and epistasis).
Heritability is estimated using the total genetic variance(Vg).
It is useful in selection of superior line from homozygous lines.
If heritability in broad sense is high, character is less influenced by environment
and vice versa.
Genetic improvement through selection will be difficult.
It is mathematically, expressed as:
H2 = Vg/Vp

5. b. Narrow sense heritability
Ratio of additive genetic variance to the total phenotypic variance.
Reliable measure as it is based on breeding value.
More useful to plant breeders because the additive component of genetic variance
determines the response to selection.
Mathematically it can be expressed as
H2 = VA/VP
Value of heritability varies from 0 ( all environment) to 1 (all genetic).

6. Factors affecting heritability estimates
The magnitude of heritability estimates depends upon on the genetic population
used, the sample size and the method of estimation.
a. Genetic population:
The amount of genotypic variance present for a trait in a population influences
estimates of heritability.
More divergent parents yield a population that is more genetically variable.
b. Sample size:
As it is difficult or impractical to measure all individuals in a large population,
heritability is estimated from sample data.
To obtain the true genetic variance for a valid estimate of the true heritability of
the trait, the sampling should be random.
c. Methods of computation:
Estimated by several methods and common methods include the variance
component method, parent-offspring regression, correlation between relatives etc.

7. Methods to estimate narrow sense heritability
• Statistical methods e.g. regression, correlation and ANOVA
1. Offspring- Parent Regression
a. Regression of offspring on one parent
b. Regression of offspring on mid parent
2. Correlation between relatives
a. Correlation between parents and offspring
b. Correlation between sibs ( full sibs or half sibs)
3. Analysis of variance ( ANOVA) or Intraclass correlation
a. Intraclass correlation between full sibs
b. Intraclass correlation between half sibs
4. Restricted Maximum Likelihood (REML) Method
 Software e.g. : WOMBAT, ASREML, SAS, BLUPF90

8. Importance of heritability in crop improvement
Helps in the construction of selection index (i.e. high heritability would likely
result in high response to selection )
To determine whether a trait would benefit from breeding. If the narrow sense
heritability for a trait is high, it indicates that the use of plant breeding methods
will likely be successful in improving the trait of interest.
Useful in predicting the effectiveness of selection.
Helpful for deciding the breeding methods to be followed for effective selection.
Estimates of a heritability serves as a useful guide to the breeder, to appreciate the
proportion of variation that is due to genotypic and additive effects.