This document provides an overview of DNA and genetics. It discusses how DNA was established as the genetic material through experiments in the 1900s and 1950s. It describes the structure of DNA as a double helix based on the work of Watson, Crick, Wilkins and Franklin. It also summarizes Mendel's laws of inheritance and how chromosomes package and transmit genetic information from one generation to the next. The document traces the history of genetics from early Greek philosophers through modern discoveries that have revolutionized our understanding of heredity and molecular biology.

1. Presentation on DNA
The primary genetic material
Presented by-
Vinay k. Dubey
M. Pharm. 1st year
(p’cology)

2. DNA- an introduction
• It stands for Deoxyribose Nucleic Acid.
• The genetic material of all living organisms, both
prokaryotes and eukaryotes , is DNA. A number of other
viruses have RNA as a genetic material.
• Research in genetics was revolutionized in 1972, when Paul
Berg constructed the 1st recombinant DNA in vitro and , in
1973, when Herbert Boyer and Stanley Cohen cloned a
recombinant molecule for the 1st time.
• The genetic material is organized into structures called
chromosomes.
• The full DNA sequence of an organism or the full DNA or
RNA sequence of virus is called its GENOME.

3. Genetics
It is the study about genetic material in living things.
The three major divisions of genetics are-
• Transmission genetics, examines the principles of heredity;
• Molecular genetics, molecular genetics deals with the gene
and the cellular processes by which genetic information is
transferred and expressed;
• Population genetics concerns the genetic composition of
groups of organisms and how that composition changes
over time and space.

4. Overview of genome

5. Pre history of genetics
The ancient Greeks gave careful consideration to human
reproduction and heredity. The Greek physician Alcmaeon
conducted dissections of animals and proposed that the
brain was not only the principle site of perception, but also
the origin of semen. This proposal sparked a long
philosophical debate about where semen was produced and
its role in heredity.
The debate culminated in the concept of pangenesis, which
proposed that specific particles, later called gemmules,
carry information from various parts of the body to the
reproductive organs, from where they are passed to the
embryo at the moment of conception.

6. Comparision of theories

7. The Rise of Modern Genetics
• Dutch spectacle makers began to put
together simple microscopes in the
late 1500s, enabling Robert Hooke
(1653–1703) to discover cells in
1665, that gave rise to the idea of
preformationism. According to
preformationism, inside the egg or
sperm existed a tiny miniature
adult, a homunculus, which simply
enlarged during development.
• Preformationism meant that all traits
would be inherited from only one
parent—from the father if the
homunculus was in the sperm or from
the mother if it was in the egg.

8. Developments in cytology in the 1800s had a strong influence
on genetics. Robert Brown described the cell nucleus in
1833. Building on the work of others, Matthis Jacob
Schleiden & Theodor Schwann proposed the concept of the
cell theory in 1839.
According to this theory, all life is composed of cells, cells
arise only from preexisting cells, and the cell is the
fundamental unit of structure and function in living
organisms. Biologists began to examine cells to see how
traits were transmitted in the course of cell division.
Charles Darwin, put the theory of evolution through natural
selection and published his ideas in On the Origin of
Species in 1856. Darwin recognized that heredity was
fundamental to evolution, and he conducted extensive
genetic crosses with pigeons and other organisms.

9. Walter Flemming observed the division of chromosomes in
1879 and published a superb description of mitosis.
August Weismann in 1890 finally laid to rest the notion of the
inheritance of acquired characteristics. He cut off the tails of
mice for 22 consecutive generations and showed that the tail
length in descendants remained stubbornly long.
Weismann proposed the germ-plasm theory, which holds that
the cells in the reproductive organs carry a complete set of
genetic information that is passed to the gametes.

10. Twentieth-Century Genetics
• The year 1900 was a watershed in the history of genetics.
• The Father of Genetics, Gregor J. Mendel conducted
breeding experiments with pea plants from 1856 to 1863
and presented his results publicly at meetings of the Brno
Natural Science Society in 1865.
• At the time, no one seems to have noticed that Mendel had
discovered the basic principles of inheritance.
• The significance of Mendel’s discovery was unappreciated
until 1900, when three botanists—Hugo de Vries, Erich von
Tschermak, and Carl Correns—began independently
conducting similar experiments with plants and arrived at
conclusions similar to those of Mendel.

11. Cause of heredity..??
• The term gene was a word that Mendel never knew. It was
not coined until 1909, when the Danish geneticist Wilhelm
Johannsen first used it. a gene as an inherited factor that
determines a characteristic.
• Mendel called them factor, Which control the phenotype of
the plant.
• Each phenotype results from a genotype developing within
a specific environment. The genotype, not the phenotype, is
inherited.
• So the gene is responsible for the inheritance of specific
character from one generation to next.

12. Mendel’s experiment
• Gene- A genetic factor (sequence of DNA) that helps to
determine a characteristic.
• Allele- One of two or more alternate forms of a gene.
• Locus -Specific place on a chromosome occupied by an
allele.
• Genotype -Set of alleles that an individual possesses.
• Heterozygote- two different alleles at a locus.
• Homozygote - two of the same alleles at a locus.
• Phenotype or trait- The appearance of a character.
• Character or characteristic - An attribute or feature.

14. Mendel’s laws
The principle of segregation (Mendel’s first law) states that
each individual diploid organism possesses two alleles for
any particular characteristic.
These two alleles segregate (separate) when gametes are
formed, and one allele goes into each gamete. Furthermore,
the two alleles segregate into gametes in equal proportions.
The concept of dominance (Mendel’s second law) states that,
when two different alleles are present in a genotype, only
the trait of the dominant allele is observed in the phenotype
& other allele is called recessive.
The theory of independent assortment states that the
daughter cells have same charecteristic as parents.

15. Chromosome theory of heredity
• The theory states that genes are located on chromosomes
was developed in the early 1900s by Walter Sutton,
The chromosome theory of inheritance shows that The two
alleles of a genotype segregate during anaphase I of
meiosis, when homologous chromosomes separate. The
alleles may also segregate during anaphase II of meiosis if
crossing over has taken place.

16. Discovery of DNA
• In late 1920, series of experiment were done for
identification of DNA as the genetic material-
• Griffith’s Transformation Experiment.
• Avery’s Transformation Experiment.
• Hershey-Chase Bacteriophage Experiment.

17. Griffith’s Transformation Experiment
• In 1928, Frederick Griffith a British medical officer, was
working with Streptococcus pneumoniae. He used two
strains of bacterium-
S strain- produced smooth shiny colony, capsulated –virulent.
R strain- rough colonies- non-virulent.
Conclusion-
He believed that the unknown agent responsible for the change
in genetic material was a protein. He called the agent the
transforming principle.

19. Avery’s Transformation Experiment
• In the 1930’s & 1940’s, American biologist Ostwald T.
Avery, with his colleagues Colin M. Macleod & Maclyn
McCarty, followed Griffith’s experiments, to identify the
transforming principle by studying the transformation of R-
type bacteria to S-type bacteria.
Conclusion-
• Result shows that DNA was the genetic material, but still
criticized.

20. Avery’s Transformation Experiment

21. The Hershey-Chase Bacteriophage Experiments

22. RNA as genetic material
• In 1956, A. Giere & G. Schramm showed that when tobacco
plants inoculated with the purified RNA of TMV.
• No lesions were produced when the RNA had been
degraded by treatment with ribonuclease & then injected
into the plant.
• In 1957, Heinz Fraenkel Conrat & B. Singer confirmed
Giere’s conclusion.
• They isolate the RNA & protein content of two distinct
TMV strains & reconstituted the RNA of one type with the
protein of the other type & vice versa.

23. TMV experiment

24. Structure of genetic materials
• A series of experiments proved that the genetic material
consist of two types of nucleic acid : DNA & RNA
• DNA is the genetic material for all living organisms & some
viruses while RNA is of remaining viruses.
• DNA & RNA are polymers (made of monomers, linked
together).
• That monomers are called as nucleotides.

25. nucleotides
A series of nucleotide sequence makes DNA & RNA.
Each nucleotides consist of three distinct part-
• A pentose sugar (five carbon ring)
• A nitrogenous base, and
• A phosphate group.
A pentose sugar-

26. A nitrogenous base-
• These are basic compounds having nitrogen in their ring.
Its having following two types-
• Purine- 9 membered, double-ringed structure.
Adenine (A) and Guanine (G)
• Pyrimidine- 6 membered, single-ringed structure.
Thymine (T),Cytosine (C) and Uracil (U).

27. Structures nitrogenous base

28. Structure of nucleotide

29. Structure of polynucleotide

30. The DNA Double Helix model
• By the chemical treatment Ervin Chargaff had hydrolyzed
the DNA of no. of organism and quantified the purines &
pyrimidine released.
• Chargaff’s rule – Amount of adenine was equal to that of
thymine and amount of guanine is equal to cytosine these
equivalencies is known as Chargaff’s rule.
• Rosalind Franklin Working with Maurice Wilkins , studied
isolated fibres of DNA by X-ray diffraction technique.
• She concluded that DNA is a helical structure with two
distinct regularities of .34 and 3.4nm along the axis of the
molecule.

31. .
In 1953, James Watson and
Francis Crick determined the
structure of DNA with the help of
Rosalind Franklin and Maurice
Wilkins as well as Erwin Chargaff.

32. Watson and Cricks Model of DNA
• DNA consists of two helical
chains wound around the same
axis in a right-handed fashion
aligned in an anti-parallel
fashion.
• There are 10.5 base pairs, or 36
Å, per turn of the helix.
• Alternating deoxyribose and
phosphate groups on the
backbone form the outside of
the helix.
• The planar purine and
pyrimidine bases of both strands
are stacked inside the helix.

33. Relationship of nucleotide

34. Different DNA structures

35. Structure of bonds in DNA
A-DNA B-DNA Z-DNA

36. Chromosomes
• The DNA in a cell is organized into physical structures
called chromosomes.
• The full DNA sequence of an organism’s haploid set of
chromosomes is its genome.
• In prokaryote, the genome is usually but not always, a
single circular chromosome. But,
• In eukaryote it is typically distributed among a number of
chromosomes in the cell nucleus.
• So it is important to understand organization of DNA
molecules in chromosomes.

37. • The total amount of DNA in the haploid genome of a
species is k/a its C value. e.g. homo sapiens have
3,400,000,000 bp of C value.
• A human cell has more than 700 times as much DNA as
does E. coli.
• Without the compacting of the 6 109 base pairs of DNA in
the diploid genome, the DNA of the chromosome of a single
human cell would be more than 2 meters long (about 6.5
feet ) if the molecules were placed end to end.
• Several packing in chromatin enable DNA to short enough
to fit into a nucleus of few micrometers in diameters.

38. Chromatin
• It is a stainable material in a cell nucleus includes DNA &
Protein. Its fundamental structure is identical in all
eukaryotes.
• Mainly two types of protein are associated with DNA in
chromatin-
Histone- small basic protien contain large amount of arginine
& lysine (with a net positive charge) so binds with DNA.
Nonhistone- all the protein associated with DNA except
histones. e.g. proteins involves in replication, repair,
transcription & recombination.
• They are acidic proteins (protein with a net negative charge)
& are likely to bind with positively charged histones in
chromatin.

39. Nucleosomes
• Five main types of histones are associated with eukaryotic
DNA are H1, H2A, H2B, H3, and H4.
• The amino acid sequence of H2A, H2B, H3, and H4
histones are highly conserved (very similar).
• These four types involves in compacting DNA & formation
of nucleosomes.
• The least compact form seen is the 10 nm chromatin fiber,
which has a characteristic ―beads
on a string morphology‖
• These beads are nucleosomes of
diameter about 10nm. Consist of
a core of 8 histones.

40. Compaction of DNA
Peter J. Russell, iGenetics: Copyright © Pearson Education, Inc., publishing as Benjamin Cummings.
10 nm chromatin is produced in the first level of packaging.
Linker DNA
H1 Histone octomer
nucleosomes

41. Condensation of chromatin
• On a nucleosome 147 bp segment of DNA is wound about
1.65 times which compact the DNA by a factor of about 6
times.
• Now a single molecule of H1 binds both to the linker DNA
at one end of the nucleosome & to the meddle of the DNA
segment wrapped around core histones.
• It gives more regular appearance & nucleosome compact
into a structure about 30 nm chromatin fiber.
• It shows by the solenoid model- has the nucleosome
spiraling helically, with about six nucleosomes per complete
turn.

42. 30-nm chromatin fiber solenoid model

43. Chromosome organization
• Chromatin packing beyond 30 nm chromatin filament is less
well understood.
• Current model shows 30-90 kb loops of DNA attached to a
proteinaceous ―scaffold‖ with a charecteristic X shape of the
paired sister chromatid.
• Loop of chromatin consist of 180-300 nucleosomes
organized into 300 nm fibers.
• An average human chromosome has approx. 2,000 looped
domains.

44. • Current information indicates that each loop is held
together at its base by nonhistone proteins that are part of the
chromosome scaffold, but details of this structure are not
known.

45. Chromosome organization

46. Chromosome organization

47. References-
• iGenetics A Molecular Approach, by Peter J. Russell,
2nd Edition.
• Genetics A Conceptual Approach by Benjamin Pierce.
• MGA 8 – Griffiths
• Internet source

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