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HYBRID VIGOUR
PREPARED BY,
ABHIJITH RAJ.R
MSc Biotechnology
HYBRID VIGOUR
HETEROSIS
This term was first used by Shull in 1914
Heterosis may be defined as superiority of an
F1 hybrid over both of its parents in terms of
yield or some other character.
Heterosis and Hybrid vigour
Hybrid vigour has been used as a synonym of
heterosis .When a homozygous inbreeds of
genetically unlike constituents are crossed
together the resulting hybrid obtained from
the crossed seeds are usually robust,vigourous,
productive and taller than the either parents.
This increased productivity or superiority over
the parents is known as Hybrid vigour.
Types of heterosis are of two types
-True heterosis(euheterosis)
-pseudo-heterosis
True heterosis
It is inherited .It can be further divided into
two types:
A)Mutational true heterosis.
B)Balanced true heterosis.
Mutational heterosis
It is the sheltering or shadowing of the
deleterious, unfavourable, often lethal,
recessive mutant genes by their adaptively
superior dominant alleles.
Balanced true heterosis
It arises out of balanced gene combinations
with better adaptive value and agricultural
usefulness.
Pseudo-heterosis
Then phenomenon of heterosis can be
explained on the basis of Genetic causes
and Physiological causes.
A) Genetic causes:
i)Dominance
ii)Over dominance
Dominance hypothesis
The theory was proposed by Davenport(1910)
Bruce(1910) and Keable and Pellew(1910).This
theory is based on the assumption that hybrid
vigour results from bringing together female
dominant genes . According to this theory ,genes
that are favourable for vigour and growth are
dominant and genes that are harmful to the
individual are recessive.
The dominant genes contributed by one parent
may complement the dominant genes
contributed by the other parent ,so that F1 will
have the more favourable combination of
dominant genes,than either parent
Over dominance hypothesis
This hypothesis was given by shull(1903) and
East(1908) independently.
-According to the supposition hybrid vigour on
the basis of heterozygosityis superior to
homozygosity.
-According to this hypothesis is there are
contrasting alleles.
-For example a1 and a2 for single locus.Each
allele produces favourable yet different effects
in the plant.
Physiological Causes
i)Greater initial capital hypothesis:
-This hypothesis was proposed by Ashby(1930)
-He studied the physiology of inbreeds and hybrids
of maize and tomato and concluded that hybrid
vigour is due to an increased initial embryo size.
He termed it as ‘Greater initial capital’.
ii)Cytoplasmic nuclear interaction
-Michelis , Shull and Lewis suggested that hybrid
vigour is the interaction of cytoplasmic and nuclear
system.
Effects or Manifestations of Heterosis
1)Quantitative Effects
2)Physiological Effects
3)Biological Effects
Heterosis in animals
i)Mule is a hybrid from a cross between
jack(Equus hemicus)and Mare(Earns equus)
which has been known since ancient times
for its well known qualities of strength and
stubbornness.
ii)Increased pork yield in pigs,more egg
laying hens , silk production in silkworms
etc.
THANK YOU

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HYBRID VIGOUR - Copy.pptx

  • 1. HYBRID VIGOUR PREPARED BY, ABHIJITH RAJ.R MSc Biotechnology
  • 2. HYBRID VIGOUR HETEROSIS This term was first used by Shull in 1914 Heterosis may be defined as superiority of an F1 hybrid over both of its parents in terms of yield or some other character.
  • 3. Heterosis and Hybrid vigour Hybrid vigour has been used as a synonym of heterosis .When a homozygous inbreeds of genetically unlike constituents are crossed together the resulting hybrid obtained from the crossed seeds are usually robust,vigourous, productive and taller than the either parents. This increased productivity or superiority over the parents is known as Hybrid vigour.
  • 4. Types of heterosis are of two types -True heterosis(euheterosis) -pseudo-heterosis
  • 5. True heterosis It is inherited .It can be further divided into two types: A)Mutational true heterosis. B)Balanced true heterosis.
  • 6. Mutational heterosis It is the sheltering or shadowing of the deleterious, unfavourable, often lethal, recessive mutant genes by their adaptively superior dominant alleles.
  • 7. Balanced true heterosis It arises out of balanced gene combinations with better adaptive value and agricultural usefulness.
  • 8. Pseudo-heterosis Then phenomenon of heterosis can be explained on the basis of Genetic causes and Physiological causes. A) Genetic causes: i)Dominance ii)Over dominance
  • 9. Dominance hypothesis The theory was proposed by Davenport(1910) Bruce(1910) and Keable and Pellew(1910).This theory is based on the assumption that hybrid vigour results from bringing together female dominant genes . According to this theory ,genes that are favourable for vigour and growth are dominant and genes that are harmful to the individual are recessive.
  • 10. The dominant genes contributed by one parent may complement the dominant genes contributed by the other parent ,so that F1 will have the more favourable combination of dominant genes,than either parent
  • 11. Over dominance hypothesis This hypothesis was given by shull(1903) and East(1908) independently. -According to the supposition hybrid vigour on the basis of heterozygosityis superior to homozygosity. -According to this hypothesis is there are contrasting alleles. -For example a1 and a2 for single locus.Each allele produces favourable yet different effects in the plant.
  • 12. Physiological Causes i)Greater initial capital hypothesis: -This hypothesis was proposed by Ashby(1930) -He studied the physiology of inbreeds and hybrids of maize and tomato and concluded that hybrid vigour is due to an increased initial embryo size. He termed it as ‘Greater initial capital’. ii)Cytoplasmic nuclear interaction -Michelis , Shull and Lewis suggested that hybrid vigour is the interaction of cytoplasmic and nuclear system.
  • 13. Effects or Manifestations of Heterosis 1)Quantitative Effects 2)Physiological Effects 3)Biological Effects Heterosis in animals i)Mule is a hybrid from a cross between jack(Equus hemicus)and Mare(Earns equus) which has been known since ancient times for its well known qualities of strength and stubbornness. ii)Increased pork yield in pigs,more egg laying hens , silk production in silkworms etc.
  • 14.