ppt

1. Heredity
INTRODUCTION…

2. Contents
• Heredity
• DNA copying- Importance
• Rules for the inheritance of traits – Mendel’s
contributions
• Monohybrid cross
• Dihybrid cross
• Expression of traits
• Sex Determination

3. DNA copying
 DNA copying: The process of making a copy of
DNA by itself along with its cellular apparatus.
Impotance:
It consists the information of protein synthesis
which make the basic body design.
It consists the hereditary information which
transfer the parental characters to young ones.
During DNA copying if any error occur, it leads to
altered body design.
Without DNA copying the reproduction process
will not complete.

4. DNA copying

5. Variations
The changes or differences
among two individuals of
the same species are called
variations.
Ex. Skin colour, Height, etc..

6. Blood Grouping

7. Inheritance of Blood Groups
 A man with blood group A marries a woman with blood
group O and their daughter has blood group O. Is this
information enough to tell you which of the traits-blood
group A or O- is dominant? Why or why not?
 No, the information is not enough because the blood group is
determined by a pair of gene. One inherited from mother and
other from father. In this case, the child inherited gene for O
blood group from mother as well as father. The genotype of
the father (Whether homozygous or heterozygous) and the
number of children in the family is not given here.
In the case given,
 Father’s Genotype may be IA
IA or
IA
IO
 Mother’s Genotype should be IO
IO

8. Blood Groups- Genotypes

10. Genetics - Terminology
 Genetics: The study of genes.
 Heredity/ Inheritance: The process of passing the traits
from parents to parents to off springs through genes.
 Variations: The changes or differences among the
individuals of the same species.
 Chromosomes: Rod shaped, specialised constricted
region of a chromatid.
 DNA: Deoxy ribo Nucleic Acid. Carries traits in a coded
form.
 Gene: It is the basic unit of inheritance. It is the
segment of DNA.
 Alleles: The alternative forms of genes.

11. Genetics - Terminology
 Homologous chromosomes: Chromosomes that are similar
in morphology (Shape and form)and genetic constitution.
 Heterologous chromosomes: Chromosomes that are
different in morphology (Shape and form)and genetic
constitution.
 Dominant trait: The character which expresses itself in (F1)
generation is a dominant trait.
 Ex. Tallness in pea plant.
 Recessive trait: The character which does not express itself
but present in a generation is called recessive trait.
 Ex. Dwarfism in pea plant.

12. Genetics - Terminology
 Homozygous: A condition in which both the genes of same type are present.
 Ex. TT- Tallness; tt – Dwarfness
 Heterozygous: A condition in which both the genes of different type are
present.
 Ex. Tt – Tallness ( T-gene of tallness, t- the gene of dwarfness. But the
character tall only expressed.
 Dominant gene: The gene that controls the appearance of an organism even
in the presence of an alternative gene.
 Ex. TT- Tallness; Tt – Tallness ( T-gene of tallness, t- the gene of dwarfness.
But the character tall only expressed. So T is dominant.
 Recessive gene: The gene that controls the appearance of an organism only
in the presence of an identical gene.
 Ex. tt – Dwarfness

13. Genetics - Terminology
 Parent generation (P): The generation that supplies
gametes to the filial generation.
 Filial generation (F): The generation that receives
gametes from the parental generation.
 Phenotype: The physical or chemical expression of an
individual.
 Genotype: The Genetic make-up (combination of alleles)
of an individual.
 Carrier: A heterozygous individual not expressing a
recessive trait but capable of passing it on to its off
spring.

14. Genetics - Terminology
 Hybrid: An off spring resulting from the
matting between individuals of two different
genetic constitutions.
 Monohybrid cross: It is the cross between two
plants which have one pair of contrasting
characters.
 Di hybrid cross: It is the cross between two
plants which have two pairs of contrasting
characters.

15. Laws of Inheritance
 Law of dominance: When two dissimilar factors of a character
are present in an organism only one expresses itself (dominant
factor) while other remain unexpressed (recessive factor)
 Law of segregation: Two factors of a character is separated at the
time of gamete formation and each gamete gets only one factor for
that character.
 Law of Independent Assortment: During the inheritance of two
or more characters, the assortment of individual traits takes place
independently during gamete formation. Thus each allele of a pair
segregates independently and each gamete formed contains one
allele of that trait. This law is inapplicable for linked genes.

16. Contrasting Characters in Pea plant

17. Monohybrid cross

18. Monohybrid cross

19. Dihybrid Cross

20. Dihybrid Cross
 In dihybrid cross, Mendel crossed two pea plants
with two pairs of contrasting characteristics, for
example- the seed colour and the seed shape. He
crossed a pea plant with round, green seeds(RRyy)
with one having yellow, wrinkled seeds(rrYY).In
F1 generation the plants obtained all are round
and yellow seeded plants.
 When he self-pollinated the F1 plants(RrYy), in F2
generation Round yellow; Round green; wrinkled
yellow and wrinkled green plants were obtained
in the ratio of 9:3:3:1. This is due to law of independent
Assortment.

21. Traits may be inherited But may NOT be
Expressed
 Mendel took pea plants with contrasting
characteristics, tall plant (TT) and dwarf
plant (tt). On cross pollination, he got all
tall plants (Tt) in F1 generation.
 Here the allele which is responsible for
dwarfness (t), is inherited but not
expressed. Because is a recessive allele it
can express only in the presence of same
identical allele.

22. Sex Determination

23. Sex Determination(Genetically)
 Humans have 46 chromosomes and are present in 23 pairs. Out
of these 23 pairs, 22 pairs are autosomes and 1 pair is sex
chromosome. Male consist XY chromosome whereas the female
consist XX chromosome. Half of the male gametes (sperms)
carry X chromosomes and other half carry Y chromosomes. All
the female gametes (ovum) carry only X chromosomes.
 A child who inherits X chromosome from the father will be a girl;
and one who inherits Y chromosome from the father will be a
boy. (Hence the sex of the new born is determined by the father.
Thus there bare 50-50 chances of a male or female child and
none of the parents may be considered responsible for sex
determination. Hence it is a matter of chance.

24. Sex Determination (Environmentally)
 (a) In some animals, the temperature at
which fertilized eggs are kept
determines whether the developing
animal in the egg is male or female. Ex-
lizard.
 (b) In some animals like the snail, an
individual can change sex under stress
and different environmental
conditions.

25. Sum Based Questions
 Two pea plants - one with round yellow seeds (RRYY) and another with wrinkled green
(rryy) seeds produce F1 progeny that have round, yellow (RrYy) seeds. When F1 plants are
self-pollinated, which new combination of characters is expected in F2 progeny? How
many seeds with these new combinations of characters will be produced when a total 160
seeds are produced in F2 generation? Explain with reason.
 Total no.of plants produced=160
 Dihybrid cross ratio=9:3:3:1
 9X+3X+3X+1X=16
 16X=160
 X=160/16; X=10
 Round, yellow: Round, green: wrinkled yellow: wrinkled green
9: 3 : 3 : 1
Round green (3x10)=30
 Wrinkled yellow (3x10)=30
 New combinations are produced because of the independent inheritance of seed shape and
seed colour trait.

26. Sum Based Questions
 Sahil performed an experiment to study the inheritance pattern of genes. He crossed tall pea plants
(TT) with short pea plants (tt) and obtained all tall plants in F1 generation.
a. What will be set of genes present in the F1 generation?
 Tt
b. Give reason why only tall plants are observed in F1 progeny.
 Traits like ‘T’ are called dominant traits, while those that behave like ‘t’ are called recessive traits.
c. When F1 plants were self - pollinated, a total of 800 plants were produced. How many of these
would be tall, medium height or short plants? Give the genotype of F 2 generation.
 Tall : Short
3 : 1
 3X+1X=800
 4X=800
 X=800/4
 X=200
 Tall=3x200=600
 Short=1x200=200
 Out of 800 plants 600 plants will be tall and 200 plants will be small (1 mark),
1 TT: 2Tt: 1tt

27. Inherited traits Vs Acquired Traits

28. References:
NCERT text book for class 10
S. Chand Publications – Lakmir Singh
ISC BIOLOGY – Dr. P. S. Verma
Dr. B. P. Pandey

29. THANK YOU!
- V.Manivannan, M.sc(Bot),M.sc(Biotech),M.Ed.,
Department of Biological Sciences…