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MOLECULAR​ ​BASIS​ ​OF​ ​INHERITANCE
DNA​ ​:​ ​Structure​ ​of​ ​Polynucleotide​ ​Chain

● DNA​ ​−​ ​Polymer​ ​of​ ​deoxyribonucleotides

● Nucleoside​ ​=​ ​Nitrogenous​ ​base​ ​+​ ​Pentose​ ​sugar​ ​(linked​ ​through​​ ​N​ ​−
glycosidic​ ​bond​)

Example​ ​−​ ​adenosine,​ ​deoxyadenosine,​ ​cytidine,​ ​etc
...


● In​ ​course​ ​of​ ​formation​ ​of​ ​polynucleotide​ ​chain,​ ​a​ ​phosphate​ ​moiety

remains​ ​free​ ​at​ ​5′​ ​end​ ​of​ ​ribose​ ​sugar​ ​(5′​ ​end​ ​of​ ​polymer​ ​chain)​ ​and
one​ ​-OH​ ​group​ ​remains​ ​free​ ​at​ ​3′​ ​end​ ​of​ ​ribose​ ​(3′​ ​end​ ​of​ ​polymer
chain)
...


Sugar-phosphate​ ​forms​ ​backbone​ ​of​ ​this​ ​helix​ ​while​ ​bases​ ​project​ ​in
wards​ ​to​ ​each​ ​other
...

Purines​ ​always​ ​pair​ ​with​ ​their​ ​corresponding​ ​pyrimidines
...


○ The​ ​helix​ ​is​ ​right-handed
...
4​ ​nm
10​ ​bp​ ​in​ ​each​ ​turn
○ The​ ​plane​ ​of​ ​one​ ​base​ ​pair​ ​stacks​ ​over​ ​the​ ​other​ ​in​ ​a​ ​double
helix
...

Packaging​ ​of​ ​DNA​ ​Helix

Packaging​ ​of​ ​DNA​ ​Helix
● Distance​ ​between​ ​two​ ​consecutive​ ​base​ ​pairs​ ​in​ ​a​ ​DNA​ ​=​ ​0
...
34​ ​×​ ​10​−9​​ ​m

● Total​ ​number​ ​of​ ​base​ ​pairs​ ​in​ ​a​ ​human​ ​DNA​ ​=​ ​6
...
34​ ​×​ ​10​−9​​ ​×​ ​6
...
2​ ​m
● 2
...

● Organisation​ ​of​ ​DNA​ ​in​ ​prokaryotes:

○ They​ ​do​ ​not​ ​have​ ​nucleus
...


○ In​ ​certain​ ​regions​ ​called​ ​nucleoids,​ ​DNA​ ​(negatively​ ​charged)​ ​is

organised​ ​in​ ​large​ ​loops​ ​and​ ​is​ ​held​ ​by​ ​some​ ​proteins​ ​(positively
charged)
...


○ Histone​ ​octamer​ ​−​ ​Unit​ ​of​ ​eight​ ​molecules​ ​of​ ​histone

○ DNA​ ​(negatively​ ​charged)​ ​winds​ ​around​ ​histone​ ​octamer
(positively​ ​charged)​ ​to​ ​form​ ​nucleosome
...
​ ​200​ ​bp​ ​of​ ​DNA
...

○ Beads​ ​on​ ​string​ ​structure​ ​in​ ​chromatin​ ​are​ ​further​ ​packaged​ ​to

form​ ​chromatin​ ​fibres,​ ​which​ ​further​ ​coil​ ​and​ ​condense​ ​to​ ​form
chromosomes​ ​during​ ​metaphase
...

Transforming​ ​Principle
● Griffith​ ​performed​ ​experiments​ ​with​ ​the​ ​bacteria​ ​Streptococcus

pneumoniae​
...

S​ ​strain​ ​Bacteria

R​ ​strain​ ​Bacteria

○ Produce​ ​smooth​ ​colonies​ ​on

○ Produce​ ​rough​ ​colonies​ ​on

○ Have​ ​a​ ​polysaccharide​ ​coat

○ Do​ ​not​ ​have​ ​a

○ Virulent​ ​(causes​ ​pneumonia)

○ Non-virulent​ ​(does​ ​not​ ​cause

culture​ ​plate

● Griffith’s​ ​experiment

culture​ ​plate

polysaccharide​ ​coat
pneumonia)

● Live​ ​R​ ​strain​ ​in​ ​the​ ​presence​ ​of​ ​heat-killed​ ​S​ ​strain​ ​produce​ ​virulence
because​ ​somehow​ ​R​ ​strain​ ​bacteria​ ​is​ ​transformed​ ​by​ ​heat-killed​ ​S

strain​ ​bacteria
...


Biochemical​ ​Nature​ ​of​ ​Transforming​ ​Material
● Avery,​ ​McLeod,​ ​and​ ​McCarthy​ ​worked​ ​to​ ​determine​ ​the​ ​biochemical
nature​ ​of​ ​genetic​ ​material​ ​responsible​ ​for​ ​transformation
...

Hershey​ ​and​ ​Chase​ ​Experiment​ ​to​ ​Confirm​ ​DNA​ ​as​ ​the​ ​Genetic
Material

● Hershey​ ​and​ ​Chase​ ​worked​ ​on​ ​bacteriophages​ ​(viruses​ ​that​ ​infect
bacteria)
...


● Hershey​ ​and​ ​Chase​ ​worked​ ​to​ ​discover​ ​whether​ ​it​ ​was​ ​a​ ​protein​ ​or
DNA​ ​that​ ​entered​ ​the​ ​bacteria​ ​from​ ​virus
...


● These​ ​radioactive​ ​phages​ ​were​ ​used​ ​to​ ​infect​ ​E
...


● E
...


● It​ ​was​ ​observed​ ​that​ ​bacteria​ ​with​ ​radioactive​ ​DNA​ ​were​ ​radioactive
while​ ​those​ ​with​ ​radioactive​ ​proteins​ ​lost​ ​their​ ​radioactivity
...
​ ​Hence,​ ​it​ ​was​ ​concluded​ ​that​ ​DNA​ ​is​ ​the​ ​genetic
material
...

● It​ ​should​ ​be​ ​chemically​ ​and​ ​structurally​ ​stable
...

● It​ ​should​ ​follow​ ​the​ ​Mendelian​ ​principles​ ​of​ ​inheritance
...

the​ ​genetic​ ​material
...


thymine
...
​ ​It​ ​acts​ ​as​ ​a​ ​genetic
material​ ​in​ ​some​ ​viruses
...


○ Chemically​ ​less

reactive,​ ​mutates

○ Mutation​ ​in​ ​RNA​ ​is​ ​faster
...


○ RNA​ ​directly​ ​codes​ ​for​ ​proteins
...
​ ​This​ ​makes​ ​RNA
unstable​ ​and​ ​degradable
...


● RNA​ ​being​ ​a​ ​biocatalyst​ ​is​ ​more​ ​reactive
...


DNA​ ​Replication​ ​with​ ​Experimental​ ​Proof​ ​Machinery​ ​and​ ​Enzymes
Involved
What​ ​is​ ​DNA​ ​Replication?
● DNA​ ​replication​ ​is​ ​the​ ​phenomenon​ ​in​ ​which​ ​a​ ​duplicate​ ​copy​ ​of​ ​DNA​ ​is
synthesised
...


● After​ ​completion​ ​of​ ​replication,​ ​the​ ​two​ ​copies​ ​so​ ​produced​ ​will​ ​have
one​ ​parental​ ​and​ ​one​ ​newly​ ​synthesised​ ​strand
...


Experiment​ ​to​ ​Prove​ ​That​ ​DNA​ ​Replicates​ ​Semi-Conservatively
● Performed​ ​by​ ​−​ ​Messelson​ ​and​ ​Stahl

● E
...


N​ ​was​ ​incorporated​ ​into​ ​newly​ ​synthesised​ ​DNA​ ​as​ ​well​ ​and​ ​the​ ​DNA

15​

became​ ​heavy​ ​DNA
...


● Then,​ ​cells​ ​were​ ​again​ ​transferred​ ​into​ ​a​ ​medium​ ​with​ 14​N​ ​as​ ​nitrogen
​
source
...


● E​ ​
...
​ ​Therefore,​ ​the​ ​DNA​ ​extracted​ ​after​ ​20
minutes​ ​had​ ​a​ ​hybrid​ ​density
...


● This​ ​implies​ ​that​ ​the​ ​newly​ ​synthesised​ ​DNA​ ​obtained​ ​one​ ​of​ ​its

strands​ ​from​ ​the​ ​parent
...


Mechanism​ ​of​ ​DNA​ ​Replication
● Replication​ ​occurs​ ​in​ ​S​ ​phase​ ​of​ ​cell​ ​cycle
...


Source​ ​of​ ​energy​ ​−​ ​Deoxyribonucleoside​ ​triphosphates​ ​(DNTPs)

● DNTPs​ ​have​ ​dual​ ​purpose​ ​−​ ​Act​ ​as​ ​substrates​ ​and​ ​provide​ ​energy​ ​also
● Replication​ ​initiates​ ​at​ ​specific​ ​regions​ ​in​ ​DNA​ ​called​ ​origin​ ​of
replication
...


● During​ ​the​ ​course​ ​of​ ​replication,​ ​two​ ​parent​ ​strands​ ​do​ ​not​ ​completely

open,​ ​but​ ​a​ ​small​ ​opening​ ​forms​ ​in​ ​which​ ​replication​ ​occurs
...

● DNA​ ​polymerase​ ​can​ ​polymerise​ ​only​ ​in​ ​one​ ​direction​ ​that​ ​is
● Therefore,​ ​replication​ ​occurs​ ​smoothly​ ​at​ ​

to​ ​

'​
...


(continuous​ ​replication,​ ​but​ ​occurs​ ​discontinuously​ ​at​ ​

to

end)

● The​ ​discontinuous​ ​fragments​ ​so​ ​formed​ ​are​ ​joined​ ​by​ ​DNA​ ​ligase
...


● During​ ​transcription,​ ​only​ ​a​ ​segment​ ​of​ ​DNA​ ​from​ ​only​ ​one​ ​of​ ​the
strands​ ​participates
...
​ ​Therefore,​ ​one​ ​DNA​ ​would​ ​end​ ​up​ ​giving​ ​rise​ ​to​ ​two
different​ ​proteins
...


Transcriptional​ ​Unit
● A​ ​transcriptional​ ​unit​ ​has​ ​primarily​ ​three​ ​regions:

○ Promoter​ ​−​ ​Marks​ ​the​ ​beginning​ ​of​ ​transcription;​ ​RNA
polymerase​ ​binds​ ​here

○ Structural​ ​gene​ ​−​ ​Part​ ​of​ ​the​ ​DNA​ ​that​ ​is​ ​actually​ ​transcribed
○ Terminator​ ​−​ ​Marks​ ​the​ ​end​ ​of​ ​transcription
Template​ ​Strand​ ​and​ ​Coding​ ​Strand
● Enzyme​ ​involved​ ​in​ ​transcription,​ ​RNA​ ​polymerase​ ​(DNA​ ​dependent
RNA​ ​polymerase),​ ​catalyses​ ​in​ ​only​ ​one​ ​direction​ ​i
...
,​ ​5′​ ​to​ ​3′
...


● The​ ​strand​ ​with​ ​polarity​ ​5′​ ​→​ ​3′​ ​acts​ ​as​ ​coding​ ​strand​ ​(which​ ​is​ ​a

misnomer​ ​since​ ​it​ ​does​ ​not​ ​code​ ​for​ ​anything)
...


Gene
● The​ ​DNA​ ​sequence​ ​which​ ​codes​ ​for​ ​tRNA​ ​or​ ​rRNA​ ​molecule​ ​defines​ ​a
gene
...
​ ​DNA​ ​is​ ​transcribed​ ​to​ ​form​ ​an​ ​mRNA,​ ​which​ ​in​ ​turn​ ​is

translated​ ​to​ ​form​ ​protein
...


● rRNA​ ​(ribosomal​ ​RNA)​ ​−​ ​These​ ​are​ ​the​ ​work​ ​benches​ ​of​ ​translation
...


Transcription​ ​Process
● Transcription​ ​has​ ​three​ ​steps​ ​−​ ​initiation,​ ​elongation,​ ​and​ ​termination
...


○ Association​ ​with​ ​initiation​ ​factor​ ​(σ)​ ​alters​ ​the​ ​specificity​ ​of​ ​RNA
polymerase​ ​to​ ​initiate​ ​the​ ​transcription
...


● Termination:

○ Termination​ ​occurs​ ​when​ ​termination​ ​factor​ ​(P)​ ​alters​ ​the

specificity​ ​of​ ​RNA​ ​polymerase​ ​to​ ​terminate​ ​the​ ​transcription
...
​ ​As​ ​the​ ​enzyme
reaches​ ​the​ ​termination​ ​region,​ ​this​ ​nascent​ ​RNA​ ​falls​ ​off​ ​and
transcription​ ​is
○ terminated
...


Therefore,​ ​translation​ ​can​ ​begin​ ​even​ ​before​ ​transcription​ ​is

completed
...


● In​ ​eukaryotes:

○ Three​ ​different​ ​kinds​ ​of​ ​RNA​ ​polymerases​ ​are​ ​present
...


RNA​ ​polymerase​ ​II​ ​transcribes​ ​hnRNA​ ​(mRNA​ ​precursor)
...


○ The​ ​precursor​ ​of​ ​mRNA,​ ​i
...
​ ​hnRNA,​ ​contains​ ​both​ ​introns​ ​and

exons
...


○ Capping​ ​−​ ​In​ ​this,​ ​methyl​ ​guanosine​ ​triphosphate​ ​is​ ​added​ ​to
the​ ​5′​ ​end​ ​of​ ​hnRNA
...


○ When​ ​hnRNA​ ​is​ ​fully​ ​processed,​ ​it​ ​is​ ​known​ ​as​ ​mRNA,​ ​which​ ​is

transported​ ​out​ ​of​ ​the​ ​nucleus​ ​to​ ​get​ ​translated
...


● George​ ​Gamow​ ​proposed​ ​that​ ​if​ ​20​ ​amino​ ​acids​ ​are​ ​to​ ​be​ ​coded​ ​by​ ​4

bases,​ ​then​ ​the​ ​code​ ​should​ ​be​ ​made​ ​up​ ​of​ ​three​ ​nucleotides
...


● Har​ ​Gobind​ ​Khorana​ ​developed​ ​a​ ​chemical​ ​method​ ​to​ ​synthesise​ ​RNA
molecules​ ​with​ ​defined​ ​combination​ ​of​ ​bases
...


● The​ ​enzyme​ ​known​ ​as​ ​Severo​ ​Ochoa​ ​enzyme​ ​(polynucleotide

phosphorylase)​ ​helped​ ​to​ ​polymerise​ ​RNA​ ​with​ ​defined​ ​sequences​ ​in​ ​a
template​ ​independent​ ​manner
...


● Salient​ ​features​ ​of​ ​genetic​ ​code:

○ Codon​ ​is​ ​triplet
...
​ ​Codons​ ​are
unambiguous
...


○ Genetic​ ​code​ ​is​ ​universal
...


○ Codons​ ​are​ ​read​ ​continuous
...


○ AUG​ ​has​ ​dual​ ​functions​ ​−​ ​Codes​ ​for​ ​Methionine​ ​and​ ​acts​ ​as​ ​a
start​ ​codon

Effects​ ​of​ ​Mutations​ ​on​ ​Genetic​ ​Code
● Mutations​ ​include​ ​insertions,​ ​deletions,​ ​and​ ​rearrangements
...
​ ​(Change​ ​Glu​ ​→​ ​Val​ ​in​ ​gene​ ​coding​ ​for​ ​beta​ ​globin​ ​chain​ ​of
haemoglobin)​ ​Such​ ​mutations​ ​are​ ​called​ ​joint​ ​mutations​
...
​ ​Such​ ​mutations​ ​are​ ​called​ ​frameshift​ ​mutations​
...


Structure​ ​of​ ​tRNA;​ ​Process​ ​of​ ​Translation;​ ​Regulation​ ​of​ ​Gene
Expression
tRNA
● tRNA​ ​is​ ​an​ ​adapter​ ​molecule
...


● tRNA​ ​has​ ​an​ ​anticodon​ ​loop​​ ​that​ ​has​ ​bases​ ​complementary​ ​to​ ​the

mRNA​ ​code​ ​and​ ​an​ ​amino​ ​acid​ ​acceptor​ ​end​​ ​where​ ​it​ ​binds​ ​to​ ​the
corresponding​ ​amino​ ​acid
...


● There​ ​are​ ​no​ ​tRNAs​ ​for​ ​stop​ ​codons
...
​ ​Amino​ ​acids​ ​are
polymerised​ ​to​ ​form​ ​a​ ​polypeptide
...


● First​ ​of​ ​all,​ ​charging​ ​of​ ​tRNA​ ​(amino-acylation​ ​of​ ​tRNA)​ ​takes​ ​place
...


● Ribosomes​ ​are​ ​the​ ​workbenches​ ​for​ ​translation
...


● Smaller​ ​subunit​ ​comes​ ​in​ ​contact​ ​with​ ​mRNA​ ​to​ ​initiate​ ​the​ ​process​ ​of
translation
...


● Untranslated​ ​regions​ ​(UTR)​ ​are​ ​the​ ​regions​ ​on​ ​mRNA​ ​that​ ​are​ ​not
themselves​ ​translated,​ ​but​ ​are​ ​required​ ​for​ ​efficient​ ​translation

process
...


● Initiator​ ​tRNA​ ​recognises​ ​the​ ​start​ ​codon
...


● tRNA​ ​moves​ ​from​ ​codon​ ​to​ ​codon​ ​on​ ​the​ ​mRNA​ ​and​ ​amino​ ​acids​ ​are
added​ ​one​ ​by​ ​one
...

(Termination)

Regulation​ ​of​ ​Gene​ ​Expression
● Regulation​ ​of​ ​gene​ ​expression​ ​could​ ​be​ ​exerted​ ​at​ ​following​ ​levels
...


● Expression​ ​of​ ​genes​ ​coding​ ​for​ ​enzymes​ ​is​ ​required​ ​only​ ​when
substrate​ ​for​ ​that​ ​enzyme​ ​is​ ​available
...
coli​ ​synthesises​ ​beta-galactosidase,​ ​only​ ​when​ ​lactose​ ​is​ ​available
...


○ The​ ​activity​ ​of​ ​RNA​ ​polymerase​ ​at​ ​a​ ​given​ ​promoter​ ​is​ ​regulated

by​ ​accessory​ ​proteins
...


○ A​ ​regulatory​ ​protein​ ​could​ ​be​ ​activator​ ​or​ ​repressor
...
​ ​Operator
is​ ​the​ ​region​ ​located​ ​adjacent​ ​to​ ​promoter
...

○ Usually​ ​operator​ ​binds​ ​to​ ​a​ ​repressor​ ​protein
...


● The​ ​elucidation​ ​of​ ​lac​ ​operon​ ​as​ ​a​ ​transcriptionally​ ​active​ ​system​ ​was
first​ ​done​ ​by​ ​geneticist​ ​Jacob​ ​and​ ​biochemist​ ​Monod
...


z

Structural

It​ ​codes​ ​for​ ​β-galactosidase
...


a

Structural

gene

It​ ​codes​ ​for​ ​transacetylase
...

● Inducer​​ ​−​ ​Lactose​ ​acts​ ​as​ ​an​ ​inducer​ ​for​​ ​lac​ ​operon​ ​since​ ​it​ ​regulates
the​ ​switching​ ​on​ ​and​ ​off​ ​of​ ​the​ ​operon
...


● For​ ​permease​ ​to​ ​be​ ​present​ ​and​ ​lactose​ ​to​ ​enter​ ​inside​ ​the​ ​cells,​ ​low
level​ ​of​ ​expression​ ​of​ ​lac​ ​operon​ ​must​ ​be​ ​present​ ​all​ ​the​ ​time
...


● This​ ​repressor​ ​binds​ ​with​ ​the​ ​operator​ ​region​ ​of​ ​operon​ ​and​ ​prevents
RNA​ ​polymerase​ ​to​ ​transcribe​ ​genes​ ​−​ ​z​,​ ​y​,​ ​and​​ ​a​ ​(negative
regulation)
...


Regulation​ ​in​ ​Presence​ ​of​ ​Inducer
● Inducer​ ​binds​ ​with​ ​the​ ​protein​ ​product​ ​of​ ​gene​ ​i​ ​(repressor)​ ​and
inactivates​ ​it
...


● In​ ​presence​ ​of​ ​all​ ​these​ ​enzymes,​ ​the​ ​metabolism​ ​of​ ​lactose​ ​proceeds
in​ ​a​ ​normal​ ​manner
...


● DNA​ ​is​ ​the​ ​storehouse​ ​of​ ​genetic​ ​information​ ​and​ ​determining​ ​its
sequence​ ​of​ ​base​ ​pairs​ ​can​ ​solve​ ​many​ ​medical,​ ​agricultural,
environmental,​ ​and​ ​evolutionary​ ​mysteries
...


● Cost​ ​of​ ​sequencing​ ​1​ ​bp​ ​=​ ​US​ ​$​ ​3

Cost​ ​of​ ​sequencing​ ​3​ ​×​ ​10​9​​ ​bp​ ​=​ ​US​ ​$​ ​9​ ​billion

● Enormous​ ​sequence​ ​data​ ​so​ ​generated​ ​would​ ​have​ ​required​ ​3300
books​ ​containing​ ​1000​ ​pages​ ​each​ ​just​ ​for​ ​a​ ​human​ ​genome
...


● Genomes​ ​of​ ​many​ ​non-human​ ​models​ ​such​ ​as​ ​bacteria,​ ​yeast,

Caenorhabditis​ ​elegans​,​ ​Drosophila​,​ ​plants​ ​(rice​ ​and​ ​Arabidopsis​)​ ​have
also​ ​been​ ​sequenced
...
e
...
​ ​It​ ​basically​ ​focuses​ ​on​ ​sequencing​ ​the​ ​part​ ​denoting​ ​a
gene
...


Genome​ ​Sequencing
● DNA​ ​from​ ​the​ ​cells​ ​is​ ​isolated​ ​and​ ​is​ ​randomly​ ​broken​ ​into​ ​fragments
of​ ​smaller​ ​sizes
...


● Cloned​ ​fragments​ ​amplify​ ​in​ ​the​ ​host
...


● Common​ ​vectors​ ​used​ ​−​ ​BAC​ ​(Bacterial​ ​artificial​ ​chromosomes)​ ​and
YAC​ ​(Yeast​ ​artificial​ ​chromosomes)

● Common​ ​hosts​ ​−​ ​Bacteria​ ​and​ ​yeasts

● Automated​ ​sequencers​ ​are​ ​used​ ​to​ ​sequence​ ​these​ ​smaller​ ​fragments
(Sanger​ ​sequencing)
...


● Alignment​ ​of​ ​the​ ​sequences​ ​is​ ​also​ ​done​ ​automatically​ ​by​ ​computer
programs
...


Preparation​ ​of​ ​Genetic​ ​and​ ​physical​ ​maps​ ​on​ ​Genome
● 2​ ​methods​ ​are​ ​used​ ​−​ ​restriction​ ​polymorphism​ ​and​ ​microsatellites
● Restriction​ ​polymorphism​ ​−​ ​Specialized​ ​enzymes​ ​called​ ​restriction

endonucleases​ ​are​ ​used​ ​to​ ​cut​ ​the​ ​genome​ ​at​ ​specialized​ ​sites​ ​called

restriction​ ​endonuclease​ ​recognition​ ​site​ ​and​ ​maps​ ​are​ ​prepared​ ​based
on​ ​it
...

Observations​ ​from​ ​HGP
● Human​ ​genome​ ​contains​ ​3​ ​×​ ​10​9​​ ​(3164
...


● An​ ​average​ ​gene​ ​consists​ ​of​ ​3000​ ​bases
...
​ ​Largest​ ​gene​ ​is​ ​dystrophin​ ​(2
...


● Total​ ​number​ ​of​ ​genes​ ​in​ ​human​ ​genome​ ​−​ ​30,000

● Over​ ​50%​ ​of​ ​the​ ​discovered​ ​genes​ ​have​ ​unknown​ ​functions
...


● Large​ ​portion​ ​of​ ​genome​ ​consists​ ​of​ ​repeating​ ​sequences
...
​ ​They​ ​are​ ​repeated​ ​over
hundred​ ​to​ ​thousand​ ​times
...


● Chromosome​ ​with​ ​most​ ​genes​ ​−​ ​Chromosome​ ​1​ ​(2968)

Chromosome​ ​with​ ​fewest​ ​genes​ ​−​ ​Chromosomes​ ​Y​ ​(231)

● SNPs​ ​(single​ ​nucleotide​ ​polymorphism)​ ​occur​ ​at​ ​about​ ​1
...
​ ​They​ ​are​ ​believed​ ​to​ ​have​ ​significance​ ​in
explaining​ ​diseases​ ​and​ ​evolutionary​ ​history​ ​of​ ​human​ ​beings
...


● 99
...
​ ​It​ ​is
the​ ​remaining​ ​0
...


● It​ ​is​ ​a​ ​really​ ​difficult​ ​and​ ​time-consuming​ ​task​ ​to​ ​sequence​ ​and
compare​ ​all​ ​3​ ​×​ ​10​9​​ ​bases​ ​in​ ​two​ ​individuals
...

Basis​ ​of​ ​DNA​ ​Fingerprinting
● Repetitive​ ​DNA​ ​is​ ​separated​ ​from​ ​bulk​ ​genomic​ ​DNA​ ​since​ ​it​ ​appears
as​ ​a​ ​distinct​ ​peak​ ​during​ ​density​ ​gradient​ ​centrifugation
...


● Satellites​ ​do​ ​not​ ​code​ ​for​ ​proteins,​ ​but​ ​have​ ​a​ ​major​ ​role​ ​to​ ​play​ ​in
DNA​ ​fingerprinting
...
​ ​A​ ​germ​ ​cell​ ​mutation
(which​ ​can​ ​pass​ ​on​ ​to​ ​the​ ​next​ ​generation​ ​through​ ​sexual
reproduction)​ ​gives​ ​rise​ ​to​ ​polymorphism​ ​in​ ​populations
...


● Polymorphisms​ ​arise​ ​normally​ ​in​ ​non-coding​ ​sequences​ ​because
mutations​ ​in​ ​non-coding​ ​sequences​ ​do​ ​not​ ​affect​ ​an​ ​individual’s
reproductive​ ​ability
...


● VNTRs​ ​are​ ​used​ ​as​ ​probes​ ​in​ ​DNA​ ​fingerprinting
...


● Fragments​ ​are​ ​separated​ ​according​ ​to​ ​their​ ​size​ ​and​ ​molecular​ ​weight
on​ ​gel​ ​electrophoresis
...


● Immobilised​ ​fragments​ ​are​ ​hybridised​ ​with​ ​a​ ​VNTR​ ​probe
...

● VNTRs​ ​vary​ ​in​ ​size​ ​from​ ​0
...


● Hence,​ ​in​ ​the​ ​autoradiogram,​ ​band​ ​of​ ​different​ ​sizes​ ​will​ ​be​ ​obtained
...
​ ​They​ ​are​ ​different​ ​in
each​ ​individual,​ ​except​ ​identical​ ​twins
...


● DNA​ ​fingerprinting​ ​forms​ ​the​ ​basis​ ​of​ ​paternity​ ​testing​ ​since​ ​a​ ​child
inherits​ ​polymorphism​ ​from​ ​both​ ​its​ ​parents
...




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