This document discusses genetic parameters and their estimation in animal breeding. It defines genetic parameters as quantities that characterize a population's statistics, such as variance and mean, which can be estimated from sample data. The key genetic parameters discussed are heritability, repeatability, and genetic correlation. Heritability quantifies the proportion of phenotypic variation attributable to genetics. Repeatability sets an upper limit for heritability and indicates how early performance predicts later performance. Genetic correlation indicates the extent to which traits are influenced by the same genes. The document outlines methods for estimating these parameters using variance components from experimental data.

1. GENETIC PARAMETERS & ITS
ESTIMATION
Narsingh Kashyap
Department of Fish Genetics & Breeding ,IFPGS, Vaniyanchavadi, Chennai

2. Introduction
Components of Variation
 Heritability
Importance of heritability
Estimation Heritability
Repeatability
Estimation of Repeatability
Genetic Correlation
Conclusion
Reference

3. • Genetic improvement occurs when the genetic merit is improved
through Several Methods. The improvement in genetic merit
refers to the overall improvement in a flock brought about by
selection for a number of traits that contribute to the flock's
breeding objective,
• Genetic Improvement - Genetic improvement is a field that can
contribute to sustainable aquaculture by improving traits like
Growth, Flesh quality, Disease resistance, Feed Conversion ratio,
Age of sexual maturation & Fecundity of individuals
Introduction

4. a) Hybridization & Crossbreeding - Crossbreeding and hybridization
can be utilized to combine favourable qualities from two genetically
different groups and to take advantage of hybrid vigour (heterosis).
b) Chromosome set manipulation - Manipulation of chromosome-sets
(polyploidization) has been accomplished for many aquatic species
through thermal and chemical shocks to developing embryos.
c) Sex manipulation - Manipulation of sex can be of advantage in
species with sexual dimorphism in important traits. It Also help to
produce monosex population.
Method of Genetic improvement

5. d) Genetic engineering - is a broad heading that includes
chromosome set manipulations and transgenesis.
Chromosome set manipulation is a group of techniques in which
sets of chromosomes in organisms are modified.
e) Selective breeding - The basic tool available for genetic
improvement, selective breeding, entails choosing the animals
with the highest genetic value as breeders for the next
generation.

6. Genetic Parameter
• Definition - Parameter a quantity (such as the mean or
variance) that characterizes a statistical population and that
can be estimated by calculations from sample data.
• genetic parameters is an important issue in animal breeding.
Parameters that are of interest are heritability, genetic
correlation and repeatability, and those are computed as
functions of the variance components.

7. Component of Variation
• The quantitative variation in a population is of three types
VP = Phenotypic variation
VG = Genotypic variation
VE = Environmental variation
FISHER 1918 , divided the genetic variance into three
components
 VA = Additive variance
 VD = Dominance variance
 VE = Epistasis variance
VP = VG + VE

8. Heritability
 Statistical definition - The Heritability is defined as the
proportion of the phenotypic variance attributed to the additive
variance.
 Second definition is more common sensical - heritability as the
extent to which genetic difference contribute to individual
difference in observed behaviour.
 It is generally expressed in percent (%)
 It is a good index of transmission of characters from parents to
their offspring.

9. Types of Heritability
Depending upon the components of variance used
as numerator in the calculation ,there are 2
definitions of Heritability
Broad sense heritability
Narrow sense heritability

10. 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
where ,Vg= genotypic variance
Vp = phenotypic variance

11. Broad sense heritability
 broad heritability (h2) separates genotypic from environmentally
induced variance: h2 = Vg Vp
 It can be estimated from both parental as well as
segregating populations
 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

12. 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
 it is calculated with the help of following formula
Heritability (h²) = VA
VP
Where VA = additive genetic variance
VP = phenotypic variance

13. NARROW SENSE HERITABILITY
 It plays an important role in the selection process in Animal
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 animal breeding in selection of elite types from
segregating populations

14.  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

15. Importance of heritability
• Heritability provides a measure of genetic variation, the
variation upon which changing the genetic composition
of the population through selection depends.
• In individuals selection , the accuracy of selection
measured in terms of the correlation between breeding
values and Phenotype values.
• Another important function of heritability is its role in
predicting of the phenotypic value of an individuals as
well predicting expected genetic improvement through
selection.
• It also predict genetic gain of an individuals'

16. Estimating Heritability From Regression
& Correlations between Relatives
When genetic and phenotypic variance is estimated for a
population, the heritability can easily be estimated
Where A = Additive genetic variance
P = phenotypic variance

17. Factors Affecting Heritability
 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
 Sample size : Large sample is necessary for accurate estimates
 Sampling methods : 2 sampling methods , Random and
Biased. The random sampling methods provide true estimates of
genetic variance and hence of heritability
 Layout or conduct of experiment : Increasing the plot size and
no. of replications we can reduce experimental error and get
reliable estimates

18. Conti.
 Method of calculation : heritability is estimated by
several methods
 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

19. • This parameter signifies intra-class correlation, usually
among the repeated expressions of a given trait for the
same individual.
• When more than one measurement of the character can
be made on each individual, the phenotypic variance can
be partitioned into variance between individuals &
variance within individuals.
• The Repeatability is introduced by Lush (1937) &
denoted by r.
Repeatability

20.  Repeatability sets an upper limit to heritability in
the broad sense.
0 ≤ h2 ≤ H2 ≤ r ≤ 1
Repeatability
r = VG+VEG
VP
where , VG= genotypic variance
VE = environmental variance
VP = phenotypic variance

21. • Repeatability sets an upper limit to heritability in the
broad sense.
• Its also useful in estimating the genetic gain in
accuracy to be expected from repeated
measurement. (By the repeating the measurement
on the same individuals, the variance due to
temporary environment differences is reduced ,that
appears in the total variance and this reduction of the
total variance represent gain in accuracy.)
• Another use of the value of the repeatability is that it
indicates extent to which a record on early
performance can be taken as an indication of the
later performance.
Importance of Repeatability

22. Source of
Variation
DF Sum of squares Means
squares
Between groups s-1 1 ∑ (Group total)2 -
CF
n
MSB
Within groups s(n-1) By difference
∑ X2
ij - CF
Divide sum of
squares by DF
MSW
Total sn-1
Where , MSB = Between group mean squares
MSW = Within group mean squares
n = number of observation
Estimation of Repeatability
The estimation of repeatability require data on repeated performance of a
representative set of individuals and is obtained as the intra-class correlation
between the repeated observations on the same individual.

23. Estimation of Repeatability
re = σ2B
σ2B + σ2W
Where σ2B = The between group variances
σ2W = The within group variances

24. • Genetic Correlation. The correlation between breeding values for
two traits is called genetic correlation and indicates to what extent
the two traits are influenced by the same genes.
• When two characters may be correlated because of common
genetic factors or common environmental factors or both.
• It is necessary to distinguish these two cause of correlation
between the characters.
• The Genetic correlation may be due to three different causes:
1) Pleiotropy
2) Linkage
3) Heterozygosity
Genetic Correlation

25. • It given ideas idea about the extent to which two characters
are under the control of the same set of genes or have the
same physiological basis for their expressions.
• If the correlation is high then probably pleiotropic is more
important; if the correlation is low the we might say that the
two traits are inherited independently.
Importance of Genetic correlation

26. Estimation of Genetic Correlation
• The estimation of genetic correlations is based on the
covariation between two characters in related in individuals in a
manner analogous to the estimation of heritabilities.
• Hazel (1943) first demonstrated the manner in which the
genetic correlation may be estimated from cross-covariance of
one trait in the progeny and another trait in the parent.
r A = Cov (X(X),Z(Y)) + Cov (X(Y),Z(X))
2√Cov (X(x),Z(X)) Cov (X(Y),Z(Y))
Where = X(X) and X(Y) is a phenotypic value of Dam
Z(X) and Z(Y) is on Progeny for the two character

28. • It govern types of selection
• Genetic parameter of a trait play a crucial role in
Designing a selection programme.
• Defining matting strategy of selected animals.
• Prediction of response to genetic improvement
in animal breeding programme.
• It govern types of mating design & breeding strategy.

29. Reference
• J P JAIN , Statistical Techniques in QUANTITATIVE GENETICS, Indian Agricultural
Statistics Research Institute , New Delhi.
• Trygve Gjedrem, Selection and Breeding Programs in Aquaculture AKVAFORSK,
Institute of Aquaculture Research AS, Norway.
• https://www.sciencedirect.com/topics/medicine-and-dentistry/genetic-
parameter
• D S Falconer & Trady F C Mackay , Introduction to quantitative genetics 4th
edition , Department of Genetics University of Edinburgh.
• N.D. Cameron, Selection Indices and Prediction of Genetic Merit in Animal
Breeding, Roslin Institute Edinburhgh UK.
• Matthew B. Hamilton , Population Genetics, Wiley – Black Well ,A John Wiley
& Sons ltd publication.
• Robert J. Brooker, Genetics Analysis & Principles, International Edition ISBN .

30. Conti,,
• E J Gardner , M J Simmons & D P Snustad , Principles of Genetics 8th
Edition , ISBN 9971-51-346-3.
• Encyclopaedia of Genetics Vol. 2, E.C.R. Reeve .
• V.S. Kirpichnikov, Genetic Bases of Fish Selection,Springer-verlag BERLIN
Heideberg New York 1981.
• SPRINGER-VERLAG ,Population Genetics and Evolution, Berlin Heidelberg
New York London, Paris Tokyo.