Heritability, Genetic advance and gxe interaction

1. HERITABILITY , GENETIC ADVANCE
AND G x E INTERACTION
SURYA CHARAN
PGS22AGR9086
Dept of Genetics and Plant Breeding

2. Heritability
•Heritability is the ratio of genotypic variance to the phenotypic variance.
•Heritability denotes the proportion of phenotypic variance that is due to genotype i.e.,
heritable .
• It is generally expressed in percent (%)
• It is a good index of transmission of characters from parents to their offspring
• Heritability H = VG/VP Or VG/VG + VE
• Where VG, VP and VE are the genotypic,phenotypic and environmental component of
variance respectively.

3. Heritability
•H2 varies from 0 (all environment) to 1 (all genetic)
• Heritability of 0 are found in highly inbred populations with no genetic variation.
• Heritability of 1 are expected for characters with no environmental variance in an
outbred population if all genetic variance is additive.
• Heritability are specific to particular populations living under specific environmental
conditions
• Heritability (h²) and Additive Variance (VA ) are fundamentally measures of how well
quantitative traits are transmitted from one generation to the next

4. TYPES OF HERITABILITY
Depending upon the components of variance used as numerator in the calculation ,there
are 2 definitions of Heritability
1. Broad sense heritability
2. Narrow sense heritability

5. Broad sense heritability
•According to Falconer, broad sense heritability is the ratio of genotypic variance to total
or phenotypic variance
• It is calculated with the help of following formula
•Heritability (h²) = Vg / Vp x 100 = Vg / Vg + Ve x100
where , Vg= genotypic variance
Vp = phenotypic variance
Ve = error variance

6. Broad sense heritability
• It can be estimated from both parental as well as segregating populations
• It express the extent to which the phenotype is determined by the genotype , so called
degree of genetic determination
•It is most useful in clonal or highly selfing species in which genotypes are passed from
parents to offspring more or less intact
• It is useful in selection of superior lines from homozygous lines

7. Narrow Sense Heritability
• It is the ratio of additive genetic variance VA to the total phenotypic variance VP (smith,
1952)
• h2 (ns) = VA/VP = VA/VG + VE
• Narrow sense heritability is reliable measure , as it is based on breeding value.
•The magnitude of narrow sense heritability is always less than or equal to broad sense
heritability.

8. Narrow Sense Heritability
•In outbreeding species evolutionary rates are affected by narrow-sense heritability
• It is the ratio of additive or fixable genetic variance to the total or phenotypic variance
•Also known as degree of genetic resemblance.
• It is calculated with the help of following formula where VA = additive genetic variance and
VP = phenotypic variance
• Heritability (h²) = VA / VP x 100
•It plays an important role in the selection process in plant breeding
• For estimation of narrow sense heritability , crosses have to be made in a definite fashion.
•It is estimated from additive genetic variance.
• It is useful for plant breeding in selection of elite types from segregating populations.

9. If heritability in broad
sense is high
It indicates
character are least
influenced by
environment
selection for
improvement of
such characters may
be useful
If heritability in broad
sense is low
The character is
highly influenced by
environmental
effects
Genetic
improvement
through selection
will be difficult

10. If heritability in narrow
sense is high
characters are
govern by additive
gene
Selection for
improvement of
such characters
would be rewarding
If heritability in
narrow sense is low
Non additive gene
action
Heterosis will be
beneficial

11. Factors affecting heritability
1.Type of genetic material : The magnitude of heritability is largely governed by the
amount of genetic variance present in a population for the character under study
2. Sample size : Large sample is necessary for accurate estimates
3.Sampling methods : Random and Biased .
The random sampling methods provide true estimates of genetic variance and hence of
heritability.

12. Factors affecting heritability
4. Layout or conduct of experiment : Increasing the plot size and no. of replications we
can reduce experimental error and get reliable estimates
5. Method of calculation : heritability is estimated by several methods
6. Effect of linkage : high frequency of coupling phase (AB/ab) causes upward bias in
estimates of additive and dominance variances .
Excess of repulsion phase linkage (Ab/aB ) leads to upward bias in dominance variance
and downward bias in additive variances

13. Genetic advance
•Improvement in the mean genotypic value of selected plants over the parental population is
known as genetic advance
•It is the measure of genetic gain under selection
•The success of genetic advance under selection depends upon three factors (Allard , 1960)
•Genetic variability : greater the amount of genetic variability in base populations higher the
genetic advance
•Heritability : the G.A. is high with characters having high heritability
•Selection intensity : the proportion of individuals selected for the study is called selection
intensity ,high selection intensity gives better results

14. The genetic advance is calculated by the following formula
GA = K x h² x δp
where , K = standardize selection differential
h² = heritability of the character under selection
δp = phenotypic standard deviation
The estimates of GA have same unit as those of the mean
The genetic advance from mixture of purelines or clones should be calculated using h²
(bs) .
From segregating populations using h² (ns).

15. If the value of Genetic
advance high
The character is
governed by
additive genes
selection will be
beneficial for such
traits
If the value of Genetic
advance low
The character is
governed by non
additive genes
heterosis breeding
may be useful

16. scale

17. Interpretation of Both Heritability and genetic advance
High heritability
and high genetic
advance
Heritability
mainly due to
additive gene
action
Selection is
effective
High heritability
and low genetic
advance
Heritability due
to non additive
gene action
Selection may
not be rewarding
Low heritability
and high genetic
advance
The character is
governed by
additive genes
Selection may
be effective
Low heritability
and low genetic
advance
The character is
governed by
non additive
genes
Selection would
be ineffective

18. G x E Interaction
•Genotype by Environment (G x E) interaction refers to the difference in the response of
genotypes to different environments.
•A conceptual G x E interaction is commonly depicted as the slope of the line when
genotype performance is plotted against an environmental gradient.
•Parallel lines indicate that there is no G x E interaction , these are very rare.
•Non Parallel , but non intersecting lines indicate that the rank of cultivar performance
stays the same across environments , these are common.
•Lines that intersect indicate that there is a change in rank of cultivars across
environments, and optimum cultivar will be local specific.

20. Role of Environment in inheritance
•Quantitative characters are considerably affected by environment. The main result of this
effect is that the relationship between genotype and phenotype is partially or completely
hidden i.e. the phenotype does not reveal the genotype.
For eg : Phenotype = Genotype+ Environment P=G+E
•If environment = 0 then phenotype = Genotype. However the effect of environment is
seldem zero. So phenotype is the joint action of Genotype and Environment.
•In crop improvement, the breeder selects plants on the basis of their phenotype. The
effectiveness of selection depend on the proportion of phenotype due to the genotype.
•Therefore, it is important to know the extent to which environment influences different
quantitative characters.
•To estimate the effect of environment on a character, large No. of strain / genotypes are
grown in a replicated trial and the data is subjected to analysis of variance as per the
experimental design used.

21. •The genotype x Environmental interaction signifies that the relative performance of
various genotype in effected by the environment.
•For eg : Performance of genotype ‘A’ may be superior to the genotype ‘B’ in one
environment but in another environment inferior to that of ‘B’.
•If G X E interaction is absent, genotype ‘A’ will be superior ‘B’ in all the environments.
•G X E affects virtually every aspect of the decision making process involved in plant
breeding programs including identification of the most relevant testing environments,
allocation of resources within a breeding program, and choice of germplasm and
breeding strategy

22. Thank you