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1. ESTIMATION OF HETEROSIS & INBREEDING
DEPRESSION
GPB 621 – PRINCIPLES OF QUANTITATIVE GENETICS
CLASS – 7
Dr. K. SARAVANAN
Professor
Department of Genetics and Plant Breeding
Faculty of Agriculture
Annamalai University

2. Dr. K. Saravanan, GPB, AU
• Shull in 1914
• Superiority of F1 hybrid over its parents.
• In other words, heterosis refers to increase of F1 in fitness and vigour
over the parental values
• Heterosis refers to the phenomenon (cause), hybrid vigour is the
phenotypic expression (effect) of the genetical phenomenon. In current
usage, heterosis and hybrid vigour are used as synonyms and
interchangeable
Heterosis

3. Dr. K. Saravanan, GPB, AU
Estimation of heterosis
The heterosis can be classified into three on the basis of
estimation.
1. Relative heterosis over mid-parent - di
2. Heterobeltiosis over better parent - dii
3. Standard heterosis/ Economic heterosis over commercial hybrid /
variety - diii

4. Dr. K. Saravanan, GPB, AU
P1 P2 F1
SP
MP BP
Relative Heterosis (di)
Heterobeltiosis (dii)
Standard
Heterosis (diii)
HETEROSIS
P1 – Parent 1 Mean Value
P2 – Parent 2 Mean Value
F1 – P1 x P2
MP – Mid Parent value
BP – Better Parent Value
SP – Standard Parent Mean value

5. Dr. K. Saravanan, GPB, AU
Relative heterosis :
• The superiority of F1 hybrid over the mid-parental value (i.e, mean
value or average of two parents involved in the cross) is known as
mid-parent heterosis, which is estimated as follows :
Relative heterosis percent (di) = X 100
where,
F1 is the mean value of F1 hybrid
MP is the average of two parents involved in the cross
Significance of Relative heterosis :
t (di) = SEd =
MP
MP
F 
1
d
SE
MP
F 
1
r
EMS
2
3

6. Dr. K. Saravanan, GPB, AU
Heterobeltiosis :
The superiority of F1 hybrid over the better parent or superior parent
Heterobeltiosis (dii)= x 100
Where,
F1 is the mean value of F1 hybrid
BP is the mean value of better parent/ Best parent of the particular
cross
Significance of Heterobeltiosis :
t (dii) = SEd =
BP
BP
F 
1
d
SE
BP
F 
1
r
EMS
2

7. Dr. K. Saravanan, GPB, AU
Standard heterosis :
• The superiority of F1 hybrid over the standard commercial variety / hybrid is known as
standard heterosis.
• The term useful heterosis was used by Meredith and Bridge (1972). It is also called as
economic heterosis. This type of heterosis is of direct practical value in plant breeding
Standard heterosis (diii)= x 100
Where,
F1 is the mean value of F1 hybrid
SV is the standard variety / hybrid
Significance of Heterobeltiosis :
t (diii) = SEd =
SV
SV
F 
1
d
SE
SV
F 
1
r
EMS
2

8. Dr. K. Saravanan, GPB, AU
INBREEDING DEPRESSION :
• To decrease in fitness and vigour due to inbreeding .
• The degree of inbreeding is measured by the inbreeding co-efficient.
• Inbreeding depression results due to fixation of unfavorable recessive
genes in F2.
• The fixation of all favorable dominant genes in one homozygous line is
impossible due to linkage between some unfavorable recessive and
favorable dominant genes.

9. Dr. K. Saravanan, GPB, AU
ESTIMATION OF INBREEDING DEPRESSION :
• The inbreeding depression is estimated when both F1 and F2 populations of the same
cross are available.
Inbreeding Depression = x 100
Where,
F1 is the mean value of F1 hybrid F2 is the mean value of F2 generation
Significance of Inbreeding Depression :
t = SEd =
Where SE1, SE2 are standard error of F1 and F2 respectively
1
2
1
F
F
F 
d
SE
F
F 2
1  2
2
2
1 SE
SE 

10. Dr. K. Saravanan, GPB, AU
• The estimation of heterosis and inbreeding depression together provide information
about the type of gene action involved in the expression of various quantitative
traits.
1. If high heterosis if followed by high inbreeding depression, it indicates the presence of non –
addivitve gene action.
2. If heterosis is followed by low inbreeding depression, it indicates presence of additive gene
action.
3. The heterosis will be high when some alleles are fixed in one parent and other alleles in the
other parent (dispersion of alleles).
4. The Genes with lack of dominance will not exhibit heterosis in F1 but may show increase in
performance in F2 (low inbreeding depression) due to fixation of genes i.e., additive gene
action.
Heterosis, Inbreeding Depression & Gene action

11. Dr. K. Saravanan, GPB, AU
Problem
A total of 15 cotton hybrids and their parents was evaluated in a RBD with four replications. The
following is the data on yield in gms. Work out the heterosis percent on all the three bases and comment on the
results. Assume P3 is the standard check.
Genotype R I R II R III R IV Total Mean
P1 x P6 64.4 60.8 51.0 58.0 234.2 58.55
P2 x P6 91.8 89.2 98.8 92.7 372.5 93.13
P3 x P6 38.1 48.2 42.5 45.8 174.6 93.65
P4 x P6 54.1 55.6 62.7 61.7 234.1 58.53
P5 x P6 74.2 85.3 78.8 84.5 322.8 80.70
P1 x P7 86.9 81.4 75.8 70.4 314.5 78.63
P2 x P7 99.8 88.2 83.3 92.3 363.6 90.90
P3 x P7 109.2 102.3 108.2 104.5 424.2 106.05
P4 x P7 99.7 106.5 112.8 110.9 429.9 107.48
P5 x P7 105.2 106.7 97.9 111.4 421.2 105.3
P1 x P8 54.4 60.8 64.8 64.1 244.1 61.03
P2 x P8 53.9 48.3 50.6 54.6 207.4 51.85
P3 x P8 93.5 93.1 89.2 83.8 359.6 89.90
P4 x P8 81.4 79.8 82.8 83.7 327.7 81.93
P5 x P8 88.6 94.2 90.8 96.2 369.8 92.45
Geno R I R II R III R IV Total Mean
P1 64.4 56.2 62.9 59.3 242.8 60.70
P2 96.9 91.4 83.8 88.4 360.5 90.13
P3 95.8 99.3 96.2 99.4 390.7 97.68
P4 62.4 70.8 73.8 69.8 276.8 69.20
P5 81.5 72.8 89.8 83.7 327.8 81.95
P6 53.2 60.6 61.6 56.8 232.2 58.05
P7 93.2 99.7 90.2 99.4 382.5 95.63
P8 85.3 89.6 79.4 84.3 338.6 84.65
Total 1827.9 1840.8 1827.7 1855.7 7352.1

12. Dr. K. Saravanan, GPB, AU
ANOVA

13. Dr. K. Saravanan, GPB, AU

14. Dr. K. Saravanan, GPB, AU
Genotype Mean
P1 x P6 58.55
P1 60.70
P6 58.05
P3 97.68
P1 x P6

15. Dr. K. Saravanan, GPB, AU
Test of significance

16. Dr. K. Saravanan, GPB, AU
Hybrid
Relative
heterosis
t value Heterobeltiosis t value
Standard
heterosis
t value
P1 x P6 -1.40 0.28 -3.54 0.63 -40.06* 11.38
P2 x P6 25.70* 6.39 3.33 0.87 -4.66 1.32
P3 x P6 20.37* 11.49 -4.12* 15.71 -4.12* 15.71
P4 x P6 -8.02 1.71 -15.42* 3.10 -40.08* 11.38
P5 x P6 15.29* 3.59 -1.53 0.36 -17.38* 4.91
P1 x P7 0.59 0.15 -17.78* 4.94 -19.50* 5.54
P2 x P7 -2.13 0.66 -4.95 1.38 -6.94 1.97
P3 x P7 9.71* 3.15 8.57* 2.43 8.57* 2.43
P4 x P7 30.41* 8.41 12.39* 3.44 10.03* 2.85
P5 x P6 18.59* 5.54 10.11* 2.81 7.80* 2.22
P1 x P8 16.03* 3.91 -27.90* 6.87 -37.52* 10.65
P2 x P8 -40.67* 11.93 -42.47* 11.13 -46.92* 13.32
P3 x P8 -1.39 0.43 -7.69* 2.26 -7.96* 2.26
P4 x P8 6.50 1.68 -3.21 0.79 -16.12* 4.58
P5 x P6 10.98* 3.07 9.21* 2.27 -5.35 1.52
Results :
P1 X P6
t value for di = 0.28
t value for dii = 0.63
t value for diii = 11.38
Tabulated ‘t’ value at 5% for df66 = 1.997

17. Dr. K. Saravanan, GPB, AU
Hybrid
Relative
heterosis
t value Heterobeltiosis t value
Standard
heterosis
t value
P1 x P6 -40.06* 11.38
P2 x P6 25.70* 6.39
P3 x P6 20.37* 11.49 -4.12* 15.71 -4.12* 15.71
P4 x P6 -15.42* 3.10 -40.08* 11.38
P5 x P6 15.29* 3.59 -17.38* 4.91
P1 x P7 -17.78* 4.94 -19.50* 5.54
P2 x P7
P3 x P7 9.71* 3.15 8.57* 2.43 8.57* 2.43
P4 x P7 30.41* 8.41 12.39* 3.44 10.03* 2.85
P5 x P7 18.59* 5.54 10.11* 2.81 7.80* 2.22
P1 x P8 16.03* 3.91 -27.90* 6.87 -37.52* 10.65
P2 x P8 -40.67* 11.93 -42.47* 11.13 -46.92* 13.32
P3 x P8 -7.69* 2.26 -7.96* 2.26
P4 x P8 -16.12* 4.58
P5 x P6 10.98* 3.07 9.21* 2.27
Results :
The hybrids P3X P7, P4 XP7 and
P5 XP7and excelled other hybrids
by recording significantly superior
heterosis on all the three bases.

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