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1. COMPONENTS OF VARIANCE- ESTIMATION OF
HERITABILITY FOR F2 GENERATION
GPB 621 – PRINCIPLES OF QUANTITATIVE GENETICS
Class – 5
Dr. K. SARAVANAN
Professor
Department of Genetics and Plant Breeding
Faculty of Agriculture
Annamalai University

2. Dr. K. Saravanan,
GPB, AU
Phenotypic Variance
Non Heritable variance
/Environmental Variance
Heritable variance /
Genotypic Variance
.
Additive gene effects
Variance due to
dominance deviation
Variance due to
epistasis
Genetic variance
Interation between genes of
the same locus (Intra allelic /
with in locus)
Interation between genes of
different loci (Inter allelic /
between loci)
Fixable
D (or)
Fully Non Fixable Partly Non Fixable
E
H (or) and

d

h 

j
i,

l

3. Dr. K. Saravanan, GPB, AU
• Gene action in different breeding programme
.
Types of Gene Action Breeding procedure to be followed
Self Pollinated Crops
1. Additive Pureline selection, Mass selection, Progeny selection and
Hybridization and selection with pedigree breeding
2. Non-additive Heterosis breeding and recombination breeding with
postponement of selection at later generations.
Cross Pollinated Crops
1. Additive Synthetic breeding, composite breeding and population
improvement by recurrent selection for gca
2. Non-additive Heterosis breeding and population improvement by recurrent
selection for sca
3. Both Additive and Non-
additive
Population improvement by Reciprocal recurrent selection

4. Dr. K. Saravanan, GPB, AU
Components of Variance (work sheet)
• Results on cotton Single Plant yield in gram in a cross between Reba
Bo50 x Laxmi.
.
Generation Mean Variance
P1 7.20 24.38
B1 20.42 294.68
F1 24.07 160.24
F2 21.66 380.30
B2 19.25 220.52
P2 9.20 44.13

5. Dr. K. Saravanan, GPB, AU
A). Estimation of “D”
Step 1. VF2 =
𝟏
𝟐
D +
𝟏
𝟒
H + E = 380.30
---------------------------------------------------
Step 2. VB1 =
𝟏
𝟒
D +
𝟏
𝟒
H + E = 294.68
VB2 =
𝟏
𝟒
D +
𝟏
𝟒
H + E = 220.52
VB1 + VB2 =
𝟏
𝟐
D +
𝟏
𝟐
H + 2E = 515.20
----------------------------------------------------
Step 3. 2VF2 = D +
𝟏
𝟐
H + 2E = 760.60
deduct VB1 + VB2 =
𝟏
𝟐
D +
𝟏
𝟐
H + 2E = 515.20
-----------------------------------------------------
𝟏
𝟐
D -- -- = 245.40
D -- -- = 490.80 ------(A)
.
Generation Mean Variance
P1 7.20 24.38
B1 20.42 294.68
F1 24.07 160.24
F2 21.66 380.30
B2 19.25 220.52
P2 9.20 44.13

6. Dr. K. Saravanan, GPB, AU
B). Estimation of “E”
Step 4.
E = 76.25 --------(B)
.
3
1
2
1 F
P
P
E
V
V
V
V



3
75
.
228
3
13
.
44
24
.
160
38
.
24




E
V
Generation Mean Variance
P1 7.20 24.38
B1 20.42 294.68
F1 24.07 160.24
F2 21.66 380.30
B2 19.25 220.52
P2 9.20 44.13

7. Dr. K. Saravanan, GPB, AU
C). Estimation of “H”
VF2 =
𝟏
𝟐
D +
𝟏
𝟒
H + E = 380.30
𝟏
𝟐
490.80 +
𝟏
𝟒
H + 76.25 = 380.30
𝟏
𝟒
H = 380.30 – 245.40 – 76.25
𝟏
𝟒
H = 58.65
H = 234.60 -------- (C)
.
Generation Mean Variance
P1 7.20 24.38
B1 20.42 294.68
F1 24.07 160.24
F2 21.66 380.30
B2 19.25 220.52
P2 9.20 44.13

8. Dr. K. Saravanan, GPB, AU
Results :
VF2 = 380.30 (Phenotypic variance)
D = 490.80 (Variance due to additive effects)
H = 234.60 (Variance due to dominance deviation)
E = 76.25 (Environmental variance)
.

9. Dr. K. Saravanan, GPB, AU
HERITABILITY FOR F2 :
• Heritability h2 (Narrow sense) =
• h2 = 245.40/380.30 = 0.6453
• h2 = 64.53 %
• Heritability h2 (Broad sense) =
𝑉𝑔
𝑉𝑝ℎ
=
𝑉𝑝ℎ−𝑉𝑒
𝑉𝑝ℎ
• h2 =
380.30 −76.25
380.30
= 0.799 = 79.90 %
.
2
2
1
2
F
V
D
h 
iance
phenotypic
effects
Additive
var
2
1
VF2 = 380.30 (Phenotypic variance)
D = 490.80 (Variance due to
additive effects)
H = 234.60 (Variance due to
dominance deviation)
E = 76.25 (Environmental
variance)

10. Dr. K. Saravanan, GPB, AU
Genotypic Coefficient of Variation :
• GCV =
• 𝑉
𝑔 = 𝑉𝑝ℎ − 𝑉
𝑒
• General Mena = F2 mean
GCV = = 80.33 %
.
100
var
X
mean
General
iance
Genotypic
100
66
.
21
05
.
304
X
VF2 = 380.30 (Phenotypic variance)
D = 490.80 (Variance due to
additive effects)
H = 234.60 (Variance due to
dominance deviation)
E = 76.25 (Environmental
variance)
Generation Mean Variance
P1 7.20 24.38
B1 20.42 294.68
F1 24.07 160.24
F2 21.66 380.30
B2 19.25 220.52
P2 9.20 44.13

11. Thank q
Dr. K. Saravanan, GPB, AU