Mendel's experiment on hybridisation and monohybrid cross

MENDEL’S EXPERIMENT ON HYBRIDIZATION&

MONOHYBRID CROSS

ByDr. ICHHA PURAKUNIVERSITY PROFESSOR IN BOTANYRANCHI WOMEN’S COLLEGE,RANCHI

Website : www,dripurak.com

04/12/23MENDEL'S EXPERIMENT1

GREGOR JOHANN MENDEL ( 1822-1884 )


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

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 generations04/12/23MENDEL'S EXPERIMENT

3


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”


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


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


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


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




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 F3Plants →F4 plants→F5 plants →→F7 plants.


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


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


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 ratioSuch 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.


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) F1 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 _____________________________________________________________________________


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


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 DwarfOn the basis of result of F1 generation of Monohybrid

crosses for all the seven traits Mendel proposed


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.


MONOHYBRID CROSS : TALL PLANT Vs DWARF PLANT



Mendel’s Monohybrid Cross ( Round seed Vs wrinkled seed ) reciprocal crosses on two sides 04/12/2322



Trait Parental cross

F1

Phenotype

F2 Phenotypes Total F2

Ratio Dominant

Recessive

Seed Shape

Round x Wrinkled

Round 5474 Round

1850 Wrinkled

7324 2.96:1

Cotyledon colour

YellowxGreen

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 Constricted

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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Mendel's experiment on hybridisation and monohybrid cross