1. MENDEL’S EXPERIMENT ON HYBRIDIZATION
&
MONOHYBRID CROSS
By
Dr. ICHHA PURAK
UNIVERSITY PROFESSOR IN BOTANY
RANCHI WOMEN’S COLLEGE,RANCHI
Website : www,dripurak.com
05/21/13MENDEL'S EXPERIMENT1
GREGOR JOHANN
MENDEL
( 1822-1884 )

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 Brief Introduction : Gregor Johann Mendel
 Hybridization
 Reasons for selecting sweet pea as Experimental Plant
 Alternative forms in sweet pea
 Steps in hybridization experiment
 Monohybrid cross
 Results of the Experiment
 Genetic Expression of Monohybrid cross
 Mendel’s conclusions
 Law of Dominance and Law of Segregation

3. Brief INTRODUCTION
GREGOR JOHANN MENDEL
( 1822-1884)
 Born on July 22,1822 at Austria in a Farmer’s Family
 School Level education at Austria
 In 1853 joined as Priest in Monastery at Brunn
 Continued Higher Education simultaneously
 In 1854 was appointed as science teacher
 He lived in a house in the premises of church
 He used to spare free time in gardening
 He became interested to know about transmission of
characters over generations 05/21/13MENDEL'S EXPERIMENT
3

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 He started his experiment of hybridization on sweet
pea in 1857 ,continued till 1865 (8 years )
 In 1865, he presented his paper before Natural History
Society, Brunn
 In 1866 the paper was published in the proceedings of the
society
 In 1900 Mendel’s work was rediscovered by Hugo de Vries
(Holland), Carl Correns (Germany) and E V Tschermak
(Austria)
 These three scientist named the laws of inheritance as
Mendel’s laws of inheritance in honour of Mendel.
 Since then Mendel is known as “Father of Genetics”

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HYBRIZATION IN PLANTS
Hybridization is frequently employed in agriculture, to make
stronger, healthier plants with desirable characteristics.
In plants hybridization is done by artificial cross pollination
For example, a cross between parent 1(Tall), with the genetic
makeup (genotype) TT, and parent 2( Dwarf), with tt,
produces progeny with the genetic makeup Tt, which is a
hybrid (the first filial generation or F1)
Hybridization was the basis of Mendel’s historic experiments
with garden peas. Inheritance studies require crossing plants
with contrasting or alternative traits

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REASONS FOR SELECTING SWEET
PEA
(Pisum sativum )
AS EXPERIMENTAL PLANT

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Pisum sativum (Sweet Pea ) is a self pollinated plant
 It is suitable for artificial cross pollination
 It bears large flowers,emasculation and pollination easy
 It is annual,results are obtained yearly
 Pure lines are easily available as it is naturally self
pollinated
 It shows several varieties showing contrasting forms of
characters

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S N Trait Alternative Forms
Dominant Recessive
1 Seed shape Round Wrinkled
2 Seed colour Yellow Green
3 Flower Colour Purple ( Red) White
4 Pod shape Inflated ( Full ) Constricted
5 Pod colour Green Yellow
6 Flower position Axial Terminal
7 Stem Height Tall (2m) Dwarf (0.5m)
Seed coat colour Grey White
ALTERNATIVE FORMS IN SWEET PEA

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STEPS IN HYBRIDIZATION EXPERIMENT
• SELECTION OF PURE BREEDING PARENTS
• Emasculation
• Bagging
• Seed setting
• Collection of seeds
• Raising of F1
generation plants
• F1
plants self pollinated
• Seed setting of F1
plants
• Collection of seeds from F1
plants
• Raising F2
generation plants
• Raising F3
Plants F→ 4
plants F→ 5
plants F7 plants.→→

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MONOHYBRID CROSS
Monohybrid cross is a cross when only one trait and its two
alternative forms are considered during hybridization experiment
1.Purple flowered male plant is crossed with white flowered female
plant
2 . Tall male plant is crossed with dwarf female plant
Steps in Monohybrid cross: Trait : Height of plant : Tall
Vs Dwarf
 Testing of parental plants for purity
 Consideration of a plant as Male parent whose pollen are used
 Consideration of a plant as female parent whose stigma is used
 From flowers of female plants anthers are removed before
anthesis- Emasculation

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 Emasculated flowers were covered in porous paper bags to avoid
undesired cross pollination
 Hybridization or artificial cross pollination was done by dusting pollen
from flowers of male plants on stigma of flowers on female plant
 Fertilized flowers were left on plants to set seeds
 Seeds were collected separately from each plant
 Seeds were sown next year to raise F1 plants
 F1 plants were left to self pollinate
 Seeds were collected separately from each plant of F1 generation
 Seeds were sown to raise F2 plants
 F2 generation plants were left to self pollinate
 Seeds of F2 plants were collected
 F3 generation plants were raised
 F4 ----------→ F5 ----------→ F6 ----------→ F7 plants were raised

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Results of the experiment ( Monohybrid Cross between
Tall male plant and female dwarf plant ) and Vice Versa
• F1
Generation – All plants were tall (Dwarfness disappeared)
• F 2
Generation – Tall and Dwarf plants both appeared in ratio approximately 3:1
• F3
Generation – Of the tall plants of F2
some plants gave tall and some
segregated again into Tall and Dwarf in 3:1 ratio and dwarf plant gave only
dwarf plant
• F4
Generation – Some tall plants of F3
generation gave Tall only and some again
segregated in 3:1 ratio
Such Monohybrid crosses were made for all the seven traits and their
alternative forms and in all cases the dominant form appeared in F1
generation, In F2 both Dominant and Recessive appeared in 3:1 ratio.

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Genetic Expression and Analysis of
Results of Monohybrid cross
______________________________________________________
_____
Parents Tall Male (TT) X Dwarf Female (tt)
_____________________________________________________________________________
Parental gametes T t
____________________________________________________________________________
Hybridisation Tt ( Zygote Seed) F→ 1
Plants (All Tall )
_____________________________________________________________________________
Hybrid Gametes (F1
) Male T(1) and t (2) Female T(3) and t(4)→ →
____________________________________________________________________________
Self Pollination TT (1,3) Tt (1,4) Tt(2,3) tt (2,4) F2
Progeny ( Tall : Dwarf,3:1)
Tall Tall Tall Dwarf
--------------------------------------------------------------------------------------------------------
↕ ↕ ↕ ↕
TT TT Tt Tt tt TT Tt Tt tt tt F3
Progeny ( Tall : Dwarf, 7:3 )
Tall Tall Dwarf Tall Dwarf Dwarf
_____________________________________________________________________________

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Genetic Expression of Monohybrid cross
(Punnet’s Square )
Parents---- TT Tall (Male ) X tt Dwarf
( Female)
Parental gametes ---- T t
Hybrid ------- Tt
F1
(All Tall)
F1
gametes Female
Male
T t
T TT Tt
t Tt tt
Phenotypic Ratio----- 3:1
Genotypic Ratio ------ 1:2:1
F2 Generation

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MENDEL’S CONCLUSION ON THE BASIS OF MONOHYBRID
CROSS
Something is transferred from one generation to other ,which
carries information for expression of the trait.
This something is particulate in nature .
Mendel called this particulate thing as Factor or Determiner
Mendelian factor is now termed as gene
Genes are present in linear fashion on specific loci(position)on
homologous chromosomes in pairs
Each gene exist in two forms or alleles and govern expression of
alternative phenotype (Allelomorphs ) such as Tall and Dwarf
On the basis of result of F1 generation of Monohybrid crosses
for all the seven traits Mendel proposed

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Law of Dominance states that in a cross pure for two
contrasting /Alternative forms of a trait , the one which expressed
itself in F1 generation is dominant and is able to suppress the
expression of other (Recessive ) form.
On the basis of result of F2 generation obtained in monohybrid
cross Mendel proposed
Law of Segregation (Law of purity of gametes/Law of
Unit characters ) states that when a pair of alleles ( Alternative
forms of a gene ) are brought together in a hybrid,they donot mix up
or blend but remain associated with each other and separate or
segregate from each other in next generation when hybrid forms
gametes.

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MONOHYBRID CROSS : TALL PLANT Vs DWARF
PLANT

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22. Mendel’s Monohybrid Cross ( Round seed Vs
wrinkled seed ) reciprocal crosses on two sides 05/21/1322

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Trait Parental
cross
F1
Phenoty
pe
F2 Phenotypes Total F2
Ratio
Dominan
t
Recessi
ve
Seed
Shape
Round x
Wrinkled
Round 5474
Round
1850
Wrinkled
7324 2.96:1
Cotyledon
colour
YellowxGree
n
Yellow 6022
Yellow
2001
Green
8023 3.01:1
Seed Coat
Colour
Grey x White Grey 705 Grey 224 White 929 3.15:1
Pod Colour Green x
Yellow
Green 428 Green 152
Yellow
580 2.82:1
Pod shape Inflated x
Constricted
Inflated 882
Inflated
299
Constrict
ed
1181 2.95:1
Position of
flower
Axial x
Terminal
Axial 651 Axial 207
Terminal
858 3.14:1
Length of
stem
Tall x Dwarf Tall 787 Tall 277 Dwarf 1064 2.84:1
Colour of
flower
Purple x
White
Purple
SUMMARY OF F2 DATA OBTAINED By MENDEL IN PEA
FROM DIFFERENT MONOHYBRID CROSSES

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