GENETICS MENDELIAN THEORY OF INHERITANE

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