In this presentation I'm trying to explain the laws Mendelian inheritance.

1. Mendelian Laws of
Inheritance
Presented by:
Sanjay Kr. Vishwakarma

2. July 20, 1822 – January 6, 1884
Austria
Father of genetics

3. Gregor Mendel's
research garden at St
Thomas' Abbey

4. Terminology
• Trait - morphological, anatomical or behavioral feature of an organism.
• Allele - different alternative forms of gene e.g., a gene for seed color has
two alleles: one for yellow and one for green.
• Homozygous – An individual in which the two copies of a gene are the
same allele.
• Heterozygous - An individual with two different alleles.
• Phenotype: observable characteristic of the some organism like color, size,
form and structure e.g., tall, short
• Genotype: The genetic constitution (gene makeup) of an organism e.g., TT,
tt, Tt

5. • F1 generation : The first filial generation; the first generation of descent
from a given mating.
• F2 generation: The second filial generation produced by crossing inter se
or by self-pollinating the F1.
• Monohybrid cross: a cross between parents differing in only one trait or
characters.
• Dihybrid cross: a cross between parents differing in two traits or
characters.
• Test cross: a cross of F1 hybrid to recessive parent type.
• Back cross: the cross of F1 hybrid to any of parents.

6. Mendel’s 7 pea traits

7. Law of Dominance
• Every gene has two alleles for a trait.
• One allele is dominant and it will always express.
• One allele is recessive and it will be suppressed by the
presence of the dominant allele.
Tall X Dwarf
TT X tt
TT, Tt = Tall
tt = dwarf

8. Law of Segregation
• During gamete formation, every paired alleles separate (segregate)
randomly so that each gamete receives one allele or the other.
• The two alleles of a gene present in the F1 do not mix with each
other; they separate and pass into different gametes in their
original form producing two different types of gametes in equal
proportion.
• The pair of alleles of each parent separate and only one allele
passes from each parent on to an offspring
• Which allele in a parent's pair of alleles is inherited is a matter of
chance.

9. • Segregation of alleles occurs during the process of gamete
formation (meiosis)
• Randomly unite at fertilization
• Mendel crossed tall and dwarf varieties of garden peas.
• All progenies of F1 generation were tall (Tt).

10. • When F1 were self-fertilized, both tall and dwarf progenies were produced in F2
generation. 75% were tall and 25% were dwarf (3:1).
Tt x Tt

11. • When F1 plants from Mendel’s experiments were crossed back
to the dwarf variety, half the progeny were tall and half dwarf.
• The phenotypic ratio observed was 1:1.
• This further demonstrated more conclusively the Principle of
Segregation.2 Tall : 2 dwarf

12. Law of Independent Assortment
• This law states that allele pairs separate independently during the
formation of gametes..
• This means that traits are transmitted to offspring independently of
one another.
• Mendel crossed plants that differ in two pairs of alleles e.g., round
yellow seeds (YYRR) and wrinkled green seeds (yyrr).
• F1 hybrids were round and yellow seeds, as expected
(YyRr).

13. • When F1 were self-fertilized, four F2 phenotypes were
observed.
• This results closely fit a ratio of 9 : 3 : 3 : 1.
• It verified the ratio in which the different gametes of the F1
hybrid were produced.
YyRr X YyRr

14. Biological Significance of Mendel’s Laws
• It showed the pattern of inheritance of the character from parent to the
offsprings.
• The Law of Independent Assortment has laid the foundation of
inheritance which claimed that different genes assorted themselves
independently of one another during gamete formation and had
established the relationship between dominant and recessive gene type.
• It also provided the reason for variation in offspring transferred from the
parents to the offspring in the form of gene (factor) present in
chromosome of gamete.

15. Multiple Choice Question

16. 1) Which of the following statements is true regarding the “law of segregation”?
a) Law of segregation is the law of purity of genes
b) Alleles separate from each other during gametogenesis
c) Segregation of factors is due to the segregation of chromosomes during meiosis
d) All of the above
Answer: d

17. 2) Alleles are
a) Alternate forms of genes
b) Linked genes
c) Chromosomes that have crossed over
d) Homologous chromosomes
Answer: a

18. 3) Which of Mendel’s law is against the theory of Blending inheritance?
a) Law of segregation
b) Law of dominance
c) Law of recessive
d) Law of independent assortment
Answer: a

19. 4) It is confirmed that phenotype of short pea plant height will be expressed only when
a) Both the parents are tall
b) One parent is tall and other short
c) The seeds are generated by selfing
d) Both parents are short
Answer: d

20. Thank You