Gregor Johann Mendel conducted experiments with pea plants from 1856 to 1864 to study heredity and variation between generations. He observed that traits are inherited as discrete units (now known as genes) that assort and segregate independently during reproduction. Mendel's work established the principles of inheritance and laid the foundations of classical genetics, though it was not widely recognized during his lifetime. His success was due to his careful experimental methods, use of pea plants as a model organism, and analysis of inheritance patterns in successive generations. Mendel's laws of inheritance explained observed patterns of dominant and recessive traits being passed from parents to offspring.

1. MENDELIAN GENETICS –
A Historical Perspective
Dr. Valli Syam

2. Tries to explain the mechanism and the basis for similarities and differences between
related individuals.
Two aspects:
Hereditary (inheritance)
Variation
Hereditary
Process of transmission of characters in living beings from parents to offspring (ie
one generation to next)
Variation
differences between individuals
Because of variation, the brothers and sisters who resemble each other in many
respects, are unique in certain feature
Hereditary variation: Differences due to genetic or genic differences
Environmental variation: Differences that arise due to environment ie. Due to
food, temperature and other external features

3. JUPITER ACADEMY
WWW.JUPITEREDUCATIONACADEMY.COM
• Born on July 22, 1822 in Czechoslovakia
• Attended courses in agriculture, pomiculture and
viniculture (1840)
• Entered Augustinian Monastery of St. Thomas at Brunn
in Austria as Priest in 1847
• In 1851, sent to University of Vienna for training in
Physics, Mathematics and Natural Sciences
• Appointed as teacher in physics and Natural sciences in
a secondary school
Gregor Johann Mendel (1822 – 1884)

4. • Started experiments with pea plants in monastery garden – Continued for 9
years from 1856 to 1864
• Published his work in “The annual proceedings of Natural History Society of
Brunn” 1865
• Made accurate predications based only on a few mathematical
relationships, without the knowledge of nucleus, chromosomes, genes or
DNA
• Not recognized during his period
• Rediscovered by three different scientists in three different corner of Europe
– Hugo DeVries (Holland), Karl Correns (Germany) and Eric Von
Tschermak (Austria)

5. Reasons for Obscurity of Mendel’s work
• Journal in which he published was Obscure
• Statistical methods are used for biological application at that time
• Discouraged by Carl Von Naegeli and Anton Kerner
• Preoccupied with Darwin’s theory of evolution “Origin of Species”
• His work with other plants didn’t work out
• Mendel – Constancy of characters of a species generation after generation –
contrary to the Theory of Evolution – Required variations for natural selection to
act upon
• Mendel – Contrasting pairs of characters exhibiting discontinuous variation –
Contemporaries were preoccupied with characters exhibiting continuous
variations.
• Phenomenon of fertilization and behaviour of chromosome during cell division
were not known at the time of Mendel

6. Reasons for Mendel’s Success
1. Method of working
• Analysis and proper planning
• Studied only one character at a time
• Carried out the experiments up to F2 and F3 generations
• Maintained Statistical records of all the experiments and analysed them carefully
• Selected genetically pure plants – purity was checked by self crossing the
progeny for several generations
• Crossing were done between the parents of pure lines having sharply visible
contrasting characters
• Grew different pure lines in separate garden plots, preventing the chances of
their mingling

7. Reasons for Mendel’s Success
2. Selection of material
Selection pea plant (Pisum sativum) for his work after long and careful thought -
advantages
• Annual Plant – Short Life cycle – possible to study several generations within a
short period
• Perfect Bisexual flowers – predominantly self pollinating
• Because of self fertilization, plants are homozygous – easy to get pure lines for
several generations
• Easy to carry out Crossing breeding by controlled pollination

8. Reasons for Mendel’s Success
3. Selection of trait
S.No. Character Trait
Dominant Recessive
1 Stem Length Tall Dwarf/Short
2 Flower Position Axial Terminal
3 Flower Colour Purple White
4 Pod Shape Inflated Constricted
5 Pod Colour Green Yellow
6 Seed Shape Round Wrinkled
7 Seed Colour Yellow Green

9. Reasons for Mendel’s Success
4. Crossing Techniques
• To prevent self fertilization, the anthers were removed from the plants
(emasculation) taken as seed parent – even before the stigma was fully mature
• The pollen from the pollen parent was dusted on the feathery stigma of
emasculated or destaminised plants
• Cross pollinated flowers were enclosed in separate bags to avoid further
deposition of pollen from other sources
• Seeds were collected separately in marked bottles. Seed character analysis –
immediate – for other analyses – seeds were grown

10. Mendel’s Procedure
Establishing pure line
Crossing procedures
Collection of Data
Observations & Presentation
Parental Generation
Hybridization
F1
Self fertilization of F1
F2
Monohybrids – one pair of contrasting
character
Dihybrids – Two pairs of contrasting characters
Trihybrids – Three pairs of contrasting
characters
Polyhybrids – more than two pairs of
contrasting characters

11. Mendel’s Observations
• F1 showed only one trait – never the other
• The trait which disappeared in F1 will reappear in F2 in the frequency of ¼
• The results of reciprocal crosses were the same

12. Mendel’s Hypotheses
• Genetic characters are controlled by unit factors or determining agents which
exist in pairs in individual organisms
• When two unlike factors for a single character are present together in a single
individual, one is dominant over the other which is said to be recessive
• During gamete formation, these unit factors segregate independently and
randomly. Each gamete will receive only one of the paired factor
• During gamete formation, segregating pairs of unit factors assort independently
of each other. Segregation of one pair – do not influence the segregation of
other pair - seen in dihybrid and polyhybrids crosses

13. REFERENCES
• Genetics – VB Rastogi – 4th Edition – Medtech Publishers -2019
• Cell Biology, Genetics, Molecular Biology, Evolution And
Ecology - P.S. Verma &V.K. Agarwal - S. Chand & Company Ltd.
2005
• Genetics A conceptual approach – Benjamin A Pierce – W.H.
Freeman & Company – 2012