The topic discussed here is Variation, Inheritance, Brief intro about Mendel & his experiments, Some terms in Genetics

2. INTRODUCTION

3. INHERITANCE & VARIATION
• The process of transmission of characters from one generation to another is known as inheritance
or heredity.
• The offsprings carrying these genetic characters can be produced either by asexual reproduction
or by sexual reproduction.
• Variations are seen among offspring that are produced by sexual reproductions, however the
offsprings produced by asexual reproduction resemble their parents and are exact copies of their
parents, lacking variations are also called clones.

4. CLONES & OFFSPRING
Characters Clone Offspring
Type of reproduction Clone is the product of asexual
reproduction
Offspring is the product of sexual
reproduction
Number of parents Clone is monoparental Offspring is derived from two
parents thus biparental
Cell division Clone is formed by mitosis.
Meiosis does not occur
Meiosis takes place prior to
formation of gametes
Resemblance Clone exactly resembles the parent Offspring differs from parent.
Recombination of genes There is no recombination of genes Due to change segregation and
chance combination of genes,
offspring exhibit genetic variations.

5. VARIATIONS
• The differences shown by the individuals of a species and also by the offsprings of the same
parents are referred to as variations.
• Variations are classified in two ways i.e.,
• As per nature of the cells it affects.
• As per degree of difference produced.

6. VARIATIONS
• As per the nature of the cell produced variations are classified into two types :
• Somatic
• Germinal or blastogenic.

7. SOMATIC VARIATIONS
• Such variations are not inherited from the parent and affect the somatic cells only. They are
acquired by the organism during its own life time and are lost with death. Hence such variations
are also called Acquired variations.
I. Environment
A. Nutrition
B. Habitat
C. Better conditions
D. Water

8. SOMATIC VARIATIONS
• II. Use and disuse of organs.
• III. Conscious efforts.

9. GERMINAL VARIATIONS
• These variations are caused due to germ cells and are thus inheritable Eg: Haemopohilia, blood
groups, Colour-blindness, baldness, eye colour etc.
• These variations appear due to
• Recombination (crossing over)
• Modification in structure of chromosomes.
• Due to change in chemical nature of genes.
• By polyploidy.
• By radiations etc.

10. CONTINUOUS VARIATIONS
• As per the degree of differences, the variations are of following types :
• Continuous
• Discontinuous.
• Continuous variations : Such variations are small and indistinct when compared to normal (average).
They are also called fluctuating variations. Such variations are unstable and non-inheritable.
• Continuous variations are of two types :
• Substantive : Such variations bring change is size, weight, colour etc. They affect the morphology. Egg
production in poultry, milk yield in cattle etc
• Meristic : Such variations bring change in certain parts of an organism Eg: number of segments get changed in
earthworm, change in number of arms in starfish, change in number of sepals and petals in a flower

11. DISCONTINUOUS VARIATIONS• Such variations are large and represent the conspicuous differences of the progeny from parents.
They are referred as mutation or sport or saltations. Mutations appear suddenly and are stable
and inheritable.
• Discontinuous variations are further classified into two types
• Substantive : Mutations bring variations in size, weight, shape, colour etc. Eg: short legged
sheep, hairless variety of dogs and cats.
• Meristic : Such variations bring change in number of certain parts in living beings Eg:
polydactyly (additional digits in fingers & toes).
• Discontinuous variations are heritable as they occur in germ cells.

12. SIGNIFICANCE OF VARIATIONS
• It constitutes the raw material for evolution.
• By the introduction of variations, useful variants of animals and plants are produced.
• Variations form the basis of heredity.
• Variations help in adaptations of organisms to changed environment.
• Variations make some individuals better suited in the struggle for existence.
• Variations provide each organism a distinct individuality.

13. HEREDITY

14. BASIC FEATURES OF INHERITANCE
• There were several theories proposed for the inheritance of characters in the next generation.
• Gregor Johann Mendel proposed his rules of inheritance in 1865.
• Five essential features of inheritance are :
• Every trait has two alternative forms.
• One alternative form of a trait may express more often than the other.
• Any alternative form a trait may remain unexpressed for many generations.
• Hidden character may reappear in original form.
• Characters or traits of any organism are expressed due to discrete particulate entities which do not get
blended or modified.

15. MENDEL’S CONTRIBUTIONS

16. GREGOR JOHANN MENDEL• Mendel for his contribution is now famous as “Father of Genetics”
• Gregor Mendel was born in 1822 in Bruno (Czechoslovakia). He finished his high school at the age
of eighteen. He completed studies in University of Vienna.
• After completing his studies he returned to Bruno (now in Czechoslovakia) in 1854, and continued to
work as a priest and as a teacher in high school.
• In 1857 he began his famous experiments on peas in monastery garden.
• Mendel presented his data and conclusion in a paper entitled “Experiments in plant hybridization”
which was published in Annual Proceedings of Natural History Society in 1866.
• Initially Mendel work was not noticed due to several reasons which include
• He published his work in an obscure journal.
• Failure of the scientists to notice his work because scientific world was at the time busy in controversy by the
Darwin’s theory of origin of species.
• His ideas were ahead of his time as the ignorance was prevalent in that period about cytological basis of
heredity.

17. MENDEL’S EXPERIMENTS
• Mendel chose garden pea (Pisum sativum) as plant material for his experiments, since it had
following advantages :
• Normally pea plant was self-fertilizing, because petals enclose the reproductive organs till fertilization.
The self fertilization through many generations helps in easily obtaining pure lines with constant trait in
pea plants.
• The pea plant was easy to cultivate and was an annual.
• Pea had many sharply defined inherited characters. Thus they possess many desirable features.
• The cross pollination and fertilization can also be achieved easily.
• The flowers are bisexual.

18. CONTRASTING CHARACTERS CHOSEN
No CHARACTER
1 Tall vine (6-7ft) Dwarf vine (3/4 -1 ½ ft)
2 Axial flower and pods Terminal flowers and pods
3 Flower colour : Purple Flower colour : White
4 Light or dark green pods Yellow pods
5 Non-constricted or full
pods
Constricted pods
6 Yellow endosperm Green endosperm
7 Round seeds Wrinkled seeds

19. MENDEL’S EXPERIMENTS

20. MENDEL’S EXPERIMENT
• Mendel made sure that his plants were purebred for the single trait he wanted to study. He did
this by letting the plant self pollinate for many generations.
• For cross-pollination, anthers have to be removed before maturity. This operation of removal of
anthers is called emasculation.
• The stigma is protected by undesired pollen by covering with a bag. This is called as Bagging.
• Pollen grains from desired plants were collected and dusted on stigma of flower in female parent.

21. WHAT DID MENDEL DO
• Mendel performed his experiments in three stages
• First, he made sure that his plants were pure bred varieties or pure line (repeated self-
fertilization).
• Second, he hybridised the plants and made several crosses by dusting the pollen of one kind on
stigma of plants of another kind. Eg: He pollinated plants from a strain whose seeds were always
round, with pollen from a strain whose seeds were always wrinkled.
• The offsprings of different parents with contrasting characters in the above example form the first
filial generation or F1 generation.
• Third stage, Mendel allowed the F1 plants to self pollinate and produced second filial or F2
generation.

22. SOME BASIC TERMS USED IN STUDIES
• Gene or Factor : The functional unit of hereditary is called gene.
• Allelomorphs or Alleles : The alternative forms of the same gene. Eg: in pure tall or pure dwarf plants same
allele is duplicated (TT and tt), while in hybrid tall both the alleles are present (Tt).
• An organism having two identical alleles is known as Homozygous. Eg: (TT or tt, RR or rr, TTRR or ttrr).
• An individual with two different alleles (Tt) will be called Heterozygous.
• Gene locus : It is the portion or regions of chromosome representing a single gene. The alleles of a gene are
present on the same gene locus on the homologous chromosome.
• Genotype : The genotype is the genetic constitution of an organism. TT, Tt and tt are the genotypes of the
organism with reference to these particular pairs of alleles.
• Phenotype : The phenotype ecpresses the characters of individuals like form, sex, colour and behaiour.
• Pure Line : Generations of homozygous individuals which produce offsprings of only one type i.e., they breed
true for their phenotype and genotype. Eg: Tall pea plants will produce only tall plants generations after
generations.

25. SOME BASIC TERMS USED IN STUDIES
• Monohybrid, Dihybrid and Polyhybrid : When only one allelic pair is considered in cross
breeding, it is called Monohybrid cross. Ex: when a Pure tall plant TT is crossed with pure dwarf
plant tt.
• Dihybrid : When two allelic characters are used for crossing, it is called Dihybrid cross Ex:
When a Tall plant with Red flower (TTRR) is crossed with Dwarf plant with White flower (ttrr).
• Polyhybrid : Involvement of more than two allelic pairs in a cross is called Polyhybrid cross.

26. SOME BASIC TERMS USED IN STUDIES
• Reciprocal cross : It involves two crosses concerning the same characteristic, but with reversed
sexes. Ex: if in first cross A is as the female parent and B is the male parent then in the reciprocal
cross A will be the male parent and B will be the female parent.
• Genome : Total set of genes (DNA) in the haploid dose of chromosomes and inherited as unit
from parents to the offspring is called genome.
• Gene pool : All the genotypes of all organisms in a population form the gene pool.

27. THANK YOU