Simple way to know about Heterosis and Inbreeding Depression

1. Heterosis
Inbreeding
Depression

2. Methods of Breeding
Autogamous species
1. Plant Introduction
2. Pureline selection
3. Mass selection
4. Pedigree method
5. Bulk method
6. Single seed descent
7. Backcross method
8. Heterosis breeding
9. Mutation breeding
10. Polyploidy breeding
11. Distant hybridization
12. Transgenic breeding.
Methods or Breeding
Allogamous species
1. Plant introduction
2. Mass and progeny
selection
3. Backcross method
4. Heterosis breeding
5. Synthetic breeding
6. Composite breeding
7. Polyploidy breeding
8. Distant hybridization
9. Transgenic breeding
Methods of Breeding
Asexually Propagated
Species
(1) Plant Introduction
(2) Clonal selection
(3) Mass selection
(4) Heterosis breeding
(5) Mutation breeding
(6) Polyploidy breeding
(7) Distant hybridization
(8) Transgenic breeding

3.  Superiority over Parents
 Confined to F1
 Genetic Control
 Reproducible
 Association with SCA
 Conceals recessive genes
 Differ from Luxuriance
 Low frequency

4. Heterosis Hybrid Vigour
Hybrid Vigour Heterosis
Negative directions
Luxuriance
Heterosis, Hybrid Vigour and Luxuriance
the increased vigour and size
generally sterile or poorly fertile
Very less adaptive significance for yield traits

5. AA BB AB
(case1)
AB
(case2)
Offspring
Parents
Mid –parent
heterosis
Best- parent
heterosis
Performance
Best-parent
Mid-parent
average heterosis
or
relative heterosis

6. Commercial
Hybrid
F1 Hybrid
Performance
Standard Heterosis
Commercial
Variety
F1 Hybrid
Economical,
Useful Heterosis

7. Manifestations of
Heterosis
Yield
Reproductive
Ability
Greater
Resistance
Better
Quality
Faster
Growth Rate
Flowering
and
Maturity
Size and
General
Vigour

8. GENETIC MODELS FOR HETEROSIS
Over-
dominance
Dominance
Epistasis

9. Proposed by Davenport in 1908 and widely
accepted
In heterozygous state, deleterious effect of
recessive allele are masked by dominant
alleles
Heterosis directly proportional to dominant
gene contributed by each parent
AABBccdd
aabbCCDD
AaBbCcDd

10. Objections
Failure in
isolation of
Inbreds as
vigorous as
hybrids
Symmetrical
distribution
in F2
Magnitude
of heterosis
Progressive
heterosis in
tetraploids
(A1A2A3A4)
Faster
inbreeding
depression
in
tetraploids

11. Proposed by Shull and East in 1908
and
coined by Hull in 1945
Stimulation of heterozygosis,
cumulative action of divergent alleles,
super dominance
Directly proportional to heterozygosity Heterosis is result of superiority of
heterozygotes over its both homozygous
parents
Overdominance
Hypothesis
AA
aa
Aa

12. Similarity
Inbreeding
Out crossing
Parental Diversity
Dominance Hypothesis
Decline in vigour & Fertility
Heterosis
Diversity is Associated
Over Dominance
Hypothesis
Decline in vigour & fertility
Heterosis
Diversity is Associated

13. Differences
ID is results of
Heterosis due to
Phenotype of
heterozygote
Dominance
Hypothesis
Homozygosity of
deleterious
recessive alleles
Masking effect of
dominant alleles
over harmful
recessive alleles
Comparable to
dominant alleles
Over
Dominance
Hypothesis
Homozygosity
itself
Heterozygosity
itself
Superior to both
homozygotes

14. Influence of one locus on the expression of another may be involved in
heterosis (Gowen, 1952)
Single
Homozygous
Recessive
Allele
Genetic
makeup
of inbred
Dramatic
heterosis
Masked by
it’s
dominant
allele

15. Epistatic interactions will lead to the maximum heterosis when the
following two conditions are met with
h (+ or -) l (+ or -) Heterosis
(+ or -)
Interacting genes
dispersed in both
parents
Absence of over
dominance
Heterosis

16. Intermediate
of single gene
product
Separate
gene
product
Combined
gene
product
Effect of two
different
tissue
Expression
of grater
number of
genes

17. Increase in size and the number of cells
Effect concerns growth regulators and enzymes
Embryo mobilize stored food materials early
Hybrid vigour resulted from

18. Heterosis leads to an increased N content in tissues increased its
photosynthetic efficiency in Rice
Heterosis in LAI in early stage have advantage during later stage of crop
growth
Net Assimilation Rate
Leaf Area Index
Root Growth
The enhanced photosynthetes produced by hybrids due to their higher LAI
may lead to production of longer root systems
Cancelation of limiting specific enzymes in hybrids leads to increase yield
Metabolic Concept

19. Fixation of Heterosis
Vegetative propagation
Apomixis
BalancedLethal System

20. Effects of inbreeding
Appearance of lethal and sub lethal alleles
Reduction in vigour
Reduction in reproductive ability
Separation of distinct lines
Increase Homozygosity
Reduction in Yield