Gregor Mendel conducted experiments with pea plants to develop his laws of inheritance. He found that traits separate and assort independently during reproduction. Dominant traits mask recessive traits in offspring, but recessive traits can still be passed down and appear in later generations. When F1 hybrids are crossed, their offspring have a 3:1 ratio of dominant to recessive traits, supporting Mendel's laws of dominance and segregation. Mendel's work established the fundamentals of genetics and heredity.

1. MENDELIAN
THEORY
OF
INHERITANCE
BY:
MRS.KEERTHI SAMUEL
ASSO.PROFESSOR
VIJAY MARIE CON

2. INTRODUCTION
• Gregor Johann Mendel – father of Modern Genetics.
• He studied approximately 29000 pea plants to demonstrate inheritance of traits
following certain laws.
• Observed characters like type of seeds , flower color and height of plants to show
that
• one in every 4 pea plants has dominant pure bred and
• 2 has hybrid and
• 1/4th shows recessive traits

3. WHY A PEA PLANT
• Flower structure of pea plant ensured self pollination
and also well defined male and female characteristics.
• Single season crop
• Emasculation and pollination of pea plants is quiet easy.
• Reproduces sexually
• In varieties available , several characters has 2
contrasting forms which were easily distinguishable
from each other

5. GENERATIONS OF PEA PLANTS
P1 generation-
parent generation
F1 – First
Generation
F2 – Second
Generation

6. MENDELS LAWS OF INHERITANCE
I. LAW OF
DOMINANCE
II LAW OF
SEGREGATION
III LAW OF
INDEPENDENT
ASSORTMENT

7. I.LAW OF DOMINENCE
• Every gene has two alleles that can code for a trait
• This law states that in a heterozygote, one trait will conceal the
presence of another trait for the same characteristic.
• The recessive allele will remain “latent,” but will be transmitted to
offspring by the same manner in which the dominant allele is
transmitted.
• However this law is not fully accepted due to
• Codominance
• Incomplete dominance
• Over dominance

8. II.LAW OF SEGREGATION
• Mendel used 2 different varieties of seed shape.
• He crossed pea plant with round seed with peaplant with wrinkled seed
WW ww –PARENT (P1)
F1 GENERATION
Ww Ww
WW
ww
Ww
Ww
-F2 GENERATION

9. F2 W w
W WW Ww
w Ww ww
• In F1 generation all round plants were
produced.
• When Crossed the F1 generation pea plants
produced 2 different types of seeds in F2
generation.
• 3 out of 4 were round
• 1 was wrinkled.
• Then F2 generation was self pollinated to get
F3 generation. In F3 generation
• 1/3rd plants were round shaped
• 2/3rd were round and wrinkled
• 1/3rd were wrinkled
• So the overall ratio of round and wrinkled
seeds is 3:1

10. INTRODUCTION
CONCLUSIONS:
• There is equal contribution of both male and female parents for the development of
characters in their offspring
• In f1 generation only dominant character is expressed. Recessive characters remain
unchanged but is not expressed.
• In F2 generation characters of both parents were expressed as 3:1
• Recessive character reappears in F2 generation which is identical to that of parents.
• Dominant character in F2 generation may be like that of parent (1/3) OR hybrid (2/3)
II.LAW OF SEGREGATION

11. INTRODUCTION
• Law of inheritance states that allele pairs seperatess independently during
gamete formation. As a result traits are transmitted to offspring independent of
each other.
• Example:
• In this Mendel crossed 2 different varieties of pea plants that differ in cotyledon and
seed color.
• 1st variety: Green cotyledon and Yellow seeds(GGYY)
• 2nd variety: yellow cotyledon and green seeds(ggyy)
• Both were hybridized
III.LAW OF INDEPENDENT ASSORTMENT

12. INTRODUCTION
• DIHYBRID CROSS
• GGYY X ggyy –P GENERATION
GgYY – F1 GENERATION
III.LAW OF INDEPENDENT ASSORTMENT

13. F2` GY Gy gY gy
GY
Gy
gY
gy
STUDENT EXERSICE

14. F2` GY Gy gY gy
GY GGYY GGYy GgYy GgYy
Gy GGyY GGyy GgyY Ggyy
gY GgYY GgYy ggYY ggYy
gy GgyY Ggyy ggYy ggyy