As a periodontist, it is of utmost importance to understand the genetic basis of inheritance in periodontal diseases be able to relate to the various polymorphisms associated with periodontal diseases. This ppt presents the basics of genetics from the point of view of future understanding of polymorphisms related to periodontal diseases.

3. MEDICAL GENETICS
 Application of genetics to
medical practice.
 Includes
 Studies of inheritance of diseases
in families
 Mapping of disease genes to
specific locations on chromosomes.
 Analysis of the molecular
mechanisms through which genes
cause disease.
 Diagnosis and treatment of genetic
diseases.

4. AS A RESULT...
 Diagnosis based on DNA is available for
inherited conditions.
 Gene therapy: Insertion of normal genes
into patients in order to correct genetic
disease.
 Genetic counselling: Information
regarding risks, prognosis and treatments
is communicated to patients and their

5. WHY IS IT IMPORTANT TO US...??
 Genetic diseases make up a large
percentage of the total disease burden..
 Genetics provides a basis for
understanding the fundamental biological
makeup of the organism hence leads to a
better understanding of the disease
process.
 Can lead to prevention of the disorder

6. A BRIEF HISTORY
 Hebrews and Greeks
 Gregor Mendel: Father of genetics

8.  CHARLES DARWIN: Theory of Evolution

9. FRANCIS GALTON

10.  Archibald Garrod (1902) described
alkaptonuria as the first inborn error of
metabolism.
 Johannsen (1909) coined the term gene to
denote the basic unit of heredity.
 H. J. Muller demonstrated the genetic
consequences of ionizing radiation in the fruit
fly.

11. OSWALD AVERY
 In 1944
 Showed that genes are composed of DNA

12. JAMES WATSON & FRANCIS CRICK
 1953

15. NUCLEUS
 Chromatin gives the nucleus a granular
appearance. Observable in nuclei of non
dividing cells.
 Just before a cell undergoes division,
chromatin condenses to form discrete,
dark staining bodies called
chromosomes.
 Chromosomes contain genes.
 Genes are composed of DNA

16.  Somatic cells
 Autosomes
 Sex chromosomes
 Gametes

17. COMPOSITION AND STRUCTURE OF DNA
 DNA molecule has 3 basic components
1. The pentose sugar deoxyribose
2. A phosphate group
3. 4 nitrogenous bases
Each DNA subunit consisting of one
deoxyribose, one phosphate group and
one base is called a NUCLEOTIDE

20. DNA COILING
 2 meter long DNA in a tiny
nucleus is coiled several times.
 First, DNA is wound around a
histone protein core to form a
nucleosome.
 About 140-150 DNA bases are
wound around each histone
core.
 20-60 bases form a spacer
element before the next
nucleosome complex.
 Nucleosomes in turn form a
helical solenoid.
 Each turn of the solenoid
contains about 6 nucleosomes.
 The solenoid is organized into
chromatin loops.
 Each of these loops contain
100 kilobases of DNA.

21. HISTONE PROTEIN

22. NAMING THE LOCATION OF A GENE ON
CHROMOSOME

25. DNA REPLICATION

27.  Nuclear Genes (∼30,000)
 Unique single copy
 Multigene families
 Classic gene families
 Gene superfamilies
 Extragenic DNA (unique/low copy number or moderate/highly
repetitive)
 Tandem repeat
 Satellite
 Minisatellite
 Telomeric
 Hypervariable
 Microsatellite
 Interspersed
 Short interspersed nuclear elements
 Long interspersed nuclear elements
 Mitochondrial (16.6 kb, 37 genes)
 Two rRNA genes
 22 tRNA genes
TYPES OF DNA SEQUENCE

28. NUCLEAR GENES
 Distribution of these genes vary between
chromosomal regions.
 Eg: Heterochromatic and centromeric
(p.32) regions are mostly non coding.
 Chromosomes 19 and 32 are gene rich
whereas 4 and 18 are relatively gene poor.

29. UNIQUE SINGLE COPY GENES
 Most human genes are unique single-
copy genes coding for polypeptides that
are involved in or carry out a variety of
cellular functions.
 These include enzymes, hormones,
receptors, and structural and regulatory
proteins.

30. MULTIGENES FAMILIES
 Many genes have similar functions, having
arisen through gene duplication events with
subsequent evolutionary divergence making up
what are known as multigene families.
 2 types
 Classic gene families that show a high degree of
sequence homology
 Gene superfamilies that have limited sequence
homology but are functionally related, having similar
structural domains.

31. EXTRAGENIC DNA
 Junk DNA
 Repetitive DNA sequences that are
predominantly transcriptionally inactive.
 Tandemly repated DNA sequences
 Satellite DNA
 Mini satellite DNA
 Telomeric DNA
 Hypervariable DNA
 Microsatellite DNA

32. MITOCHONDRIAL DNA
 Circular dsDNA
 Codes for 37 genes
 2 types of RNA
 22 tRNA
 13 protein subunits
 Cytochrome b and
cytochrome oxidase
used for oxidative
phosphorylation
 Maternal inheritance

33. PSEUDOGENES
 Closely resemble known structural genes
but are not functionally expressed.
 Thought to have arisen in two main ways:
 By genes undergoing duplication events that are
rendered silent through the acquisition of
mutations in coding or regulatory elements
 As the result of the insertion of complementary
DNA sequences, produced by the action of the
enzyme reverse transcriptase on a naturally
occurring messenger RNA transcript, that lack
the promoter sequences necessary for
expression.

34. FROM GENES
TO
PROTEINS

36. TRANSCRIPTION
 Process by which an RNA sequence is
forms from a DNA template.
 Type of RNA produced is mRNA.
 To initiate- RNA polymerase II binds to a
promoter site on the DNA.
 A promoter is a nucleotide sequence that
lies just upstream of a gene.
 The RNA polymerase then pulls a portion
of the DNA strands apart from each other
exposing unattached DNA bases.

37.  One of the 2 DNA strands provide the
template for the sequence of mRNA
nucleotides.
 RNA molecule can be synthesised only in
the 5’ to 3’ direction.
 Antisense strand: Template DNA strand
 Sense strand: DNA strand that does not
serve as the template.

38.  In the process of
transcription, RNA
polymerase II binds to
a promoter site near
the 5' end of a gene on
the antisense strand
and, through
complementary base
pairing, helps to
produce an mRNA
strand from the
antisense DNA strand.

40. SOON AFTER RNA SYNTHESIS BEGINS
 5' end of the growing RNA molecule is capped by the
addition of a chemically modified guanine nucleotide.
 Helps to prevent the RNA molecule from being
degraded during synthesis, and later it helps to
indicate the starting position for translation of the
mRNA molecule into protein.
 Transcription continues until a group of bases called
a termination sequence is reached.
 Near this point, a series of 100 to 200 adenine bases
are added to the 3' end of the RNA molecule.
 This structure, known as the poly-A tail, may be
involved in stabilizing the mRNA molecule so that it is
not degraded when it reaches the cytoplasm.
 This final mRNA molecule is termed the primary
transcript

41. TRANSCRIPTION AND REGULATION OF GENE
EXPRESSION
 RNA polymerase cannot locate the
promoter region on its own.
 It is also incapable of producing
significant quantities of mRNA by itself.

42.  Transcription factors are required for the
transcription of DNA to mRNA.
 General transcription factors are used by all
genes, and specific transcription factors
help to initiate the transcription of genes in
specific cell types at specific points in time.
 Transcription is also regulated by enhancer
and silencer sequences, which may be
located thousands of bases away from the
transcribed gene

45. DNA BINDING MOTIFS...
 Configurations in the transcription-factor
protein that allow it to fit snugly and
stably into a unique portion of the DNA
double helix

47. EUCHROMATIN & HETEROCHROMATIN
 Gene activity can also be related to patterns of
chromatin coiling or condensation.
 Euchromatin: Decondensed, or open, chromatin
regions.
 Typically characterized by histone acetylation, the
attachment of acetyl groups to lysine residues in the
histones.
 Acetylation of histones reduces their binding to DNA,
helping to decondense the chromatin so that it is
more accessible to transcription factors.
 Euchromatin is thus transcriptionally active.
 Heterochromatin: Usually less acetylated, more
condensed, and transcriptionally inactive.

49. GENE SPLICING

51. THE GENETIC CODE

52.  Process in which mRNA provides a
template for the synthesis of a
polypeptide.

53. TYPES OF RNA
 mRNA
 tRNA
 rRNA

54.  Cloverleaf structure
 30 cytoplasmic tRNA.
 80 nucleotides
 Acceptor stem (7bp)
 D(dihydrouridine) loop
(4bp)
 Anticodon loop (5bp)
 Variable loop
 T arm (5bp)

55.  Helps to bind mRNA
and tRNA to the
ribosome.
 40s and 60s

56. TRANSLATION
 The ribosome first binds to an initiation
site on the mRNA sequence
 AUG  Methionine
 This AA is usually removed from the
polypeptide before the completion of
polypeptide sequence.
 The ribosome then binds the tRNA to its
surface so that base pairing can occur
can occur between tRNA and mRNA.

57.  The AAs are covalently bond by reacting
with ATP to the specific tRNA molecule by
the activity of aminoacyl tRNA
synthetase.
 The ribosome with its associated rRNAs
move along the mRNA, the AA linking up
with formation of peptide bonds through
the action of peptidyl transferase to form
a polypeptide chain.

60.  Before a newly synthesised polypeptide
can begin its existence as a functional
protein, it often undergoes further
processing.

63. OSTEOGENESIS
IMPERFCTA:
AN INHERITED
COLLAGEN
DISORDER

64. PROTEINS

65. REFRENCES
 Medical Genetics (By: Jorde et al)
 Emery’s Elements of Medical Genetics (By: Turnpenny et
al)
 http://www.nature.com/scitable/topicpage/discovery-of-
dna-structure-and-function-watson-397
 http://www.ncbi.nlm.nih.gov/Class/MLACourse/Modules/M
olBioReview/central_dogma.html
 http://www.nature.com/scitable/topicpage/translation-dna-
to-mrna-to-protein-393
 http://www.nature.com/scitable/definition/genetic-code-13
 Molecular Biology of Periodontium (By: KV Arun)