GREGOR JOHANN MENDEL (1822 – 1884 ) :
Biography:-
·
Johann Mendel
was born on 22nd July 1822
in a village called Heinzendorf.
·
His father was
Austrian poor farmer.
·
Mendel’s
education began in an upper elementary school in Leopnik, the place about 22 km. away from his village.
·
He was clever
and sent to the Traphan high school in
1834.
·
He completed
his graduation with good record in 1840.
·
He joined the “philosophical Institute at olmitz in 1843.
·
He joined the university of vienna in 1850.
·
In 1854, he joined the Brun modern school as a teacher and
taught mathematics & natural science.
·
He began his
famous hybridization experiments on garden pea plant in 1856.
·
He performed
experiment on pea plant (Pisum sativum) for 8 years.
·
He presented
his work in paper entitled “ Experiments
in plant hybridization” at the meeting of the Natural History Society of
Brun in 1865
·
He was also published Journal i.e. “Annual proceedings of Natural History
Society” in 1866.
·
Unfortunately, his work remained unknown for 35 years.
·
Mendel died in 1884 he was really respected priest,
teacher but nobody could be recognized him as a genius scientist.
Ø After 35 years in 1900 century his work was
rediscovered by three scientist; Hugo De
vries from Holland, Karl Correns
from Germany & E. Tschermak from
Austria independently.
Ø De vries found research paper of mendel &
he published in his flora in 1901.
Ø During the time of mendel, mitosis &
meiosis were not discovered but Hugo De vries’s days mitosis & meiosis were
discovered & scientist realized the greatest work of Mendel.
Ø Based on the
data of Mendel, Corren scientist from Germany postulated three laws of
inheritance are known as Mendel law’s of
inheritance and new branch of biology i.e. genetics came in biological science.
Mendel’s Experiments:
Selection of material :
Mendel selected garden pea plant for his experimental material. Mendel selected
pea plant for his experiment material because of following reasons or
characteristics.
1.
Pea plant is
small, annual.
2.
Life spane is short.
3.
Life cycle
completed within 3 to 4 months.
4.
Mendel could
grow three generations in a year.
5.
Garden pea
plant produces many seeds.
6.
Pea plant is bisexual so easily self
pollinated.
7. Plant is small so it requires small area.
8.
Pea plant
having several pairs of contrasting characters; like Tall and Dwarf plant, colored(red) flower
& white flower, Yellow & green seeds, Round & wrinkled shape of
seed, pod colour is green & yellow, pod shape and flower position.
In
this way Mendel had selected 7 pairs of
Contrasting /opposite characters.
[Note:
Mendel considered those characters are much more commonly express in
plant known as dominant characters & those are not commonly found or
express called them recessive characters.]
GENETIC TERMINOLOGY :
Ø Emasculation :- Removal of
anther before anthesis.
Ø Character :- It is the feature of an organism. eg. height of stem.
Ø Trait :- An inherited character which is noticable eg.
Tall & dwarf.
Ø Factor : It is the unit
of heredity or particle present on the chromosome responsible for inheritance
& expression of particular character.
Ø Factor term is coined by Mendel. These factors
transmit from one generation to another generation and determined the
particular character.
Ø Gene:- It is the
segment of DNA which is responsible for inheritance & expression of a
particular characters. The term gene is used by Johannsen.
Ø Alleles & Allelomorphs:- It is the two
or more alternative forms of gene (factor) are called alleles. The term alleles
were coined by Bateson.
Ø Dominant :-
It is an allele or gene which expresses its trait either in presence of alternative allele or even if it
is present alone. Eg. Tt = Tall or TT
Tall.
Ø Recessive :- It is an allele or gene which is not
expresses its trait if it is present in single form or in presence of
alternative allele. It can only express its trait in homozygous recessive
condition Eg. tt for Dwarfness.
Ø Phenotype :- The external
appearance of an individual for any trait is called phenotype for that trait
Eg. trait like Tall or Dwarf for the plant.
Ø Genotype :- Genetic
constitution of an individual with respect to single character or set of
characters. If the genotype of plant for
set of characters like Tall plant with yellow seed and Dwarf plant with green
seed will be TT YY (homozygous dominant) Tt Yy (heterozygous or Dihybrid ) and
Dwarf plant with green seed having (ttyy) genotype.
Ø Homozygous :- An individual
possessing similar alleles for particular trait is called as homozygous
condition eg. TT = Tall plant or tt = Dwarf plant. Homozygotic plant producess only one type of
gamete.
Ø Heterzygous : An individual
possessing dissimilar alledels for particular trait is called as heterozygous
condition or called hybrid for that trait. eg. Tt (
hybrid) Heterozygotic plant or hybrid plant producess
two type of gametes.
Ø Pure line :- It is an
individual or group of individuals which are homozygous or true breeding for
perticular trait.
Ø Hybrid :- It is
heterozygous individual produced from pure line parents having one or more
contrasting traits.
Ø Monohybrid: A hybrid
produced from monohybrid cross is called as monohybrid eg. Tt (monohybrid)
Ø Dihybrid :- A hybrid
produced from dihybrid cross is called as dihybrid eg. TyRr (Tall plant and
round seed).
Ø F1 Generation :- (F stands for filial
meaning offspring produced in sexual reproduction)
(In Latin word fillin means a son) Individual
produced from parental generation called
generation.
Ø P1 parantal generation :- Plants are
used for crossing which are true breeding ie. Pure line called as P generation.
Ø F2 generation :- Progeny or
individuals produced from
generation
called as
progeny and generation called as
generation.
Ø Punnett square / checker board:- It is the board like diagram used for showing
possibilities of zygotic combination of a particular cross. This board is
called as punnett square because Punnett
scientist had made this board.
Ø Homologous chromosomes:- It is the pair
of chromosomes which are morphologically and structurally same & present in
diploid cell. Such type of chromosomes are called as homologous chromosomes or
homologues.
Procedure
of experiment:-
- Mendel had a systematic approach in his hybridization experiment.
- He was very methodical. He first studied inheritance of just one trait at a time.
- Initially he carried out monohybridization considering a single pair of contrasting character.
- After completing the monohybridization he carried out dihybridization & trihybridization by considering two & three pairs of contrasting characters respectively.
- Mendel carefully compile the data obtained from hybridization experiments & was able to derive single ratio such as 3:1, 1:2:1, 9:3:3:1, 1:1 for his experiment.
·
Mendel experiment involves three steps-
o
Step
1-Selection of parents and obtaining pure line:
1. Mendel himself
ensured that the selected male & female parent plants are truly breeding or
not.
2. Parent plant then selected as a parent plant ensures
for three generation by selfing.
o
Step
2-Artificial cross of selected parents to raise
generation :
1. Mendel first
emasculated the flower for artificial cross.
2. He selected as
a female parent of those plants whose stamen are removed with the help of
forceps.
The shape of
carolla of pea plant is papilinaceous type having five petals. one large
standard, two are wings at middle & inner two petals are joinet called carina/ keel. In pea plant stamens are
( 9) +1 condition it can be easily removed.
( 9) +1 condition it can be easily removed.
o
Step
3–Selfing of
- hybrids to raise
- generation:
Mendel allowed the
natural self pollination of 
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