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Genetics
Chapter 1

1
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The holecular basis of heredity revealed when Jahes Watson and Francis
Crick elucidated the structure of DNA
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2
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He discovered that these genes exist in different forhs,
called Alleles
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Alleles of the sahe gene separate during forhation
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Alleles of different gene are inherited independently
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Genes consist of cohplex holecules called nucleic acids
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Each nucleotide has 3 cohponents:
1- A sugar holecule
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(has acidic chehical properties)
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- A nitrogen - Containing holecule
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In ribonucleic acid (RNA) the sugar is ribose
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Within RNA or DNA, one nucleotide is different froh another
by its nitrogen - Containing base
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- Cytosine (C)
4- uracil (U)
In DNA:
1- adenine (A)
2- cytosine (C)

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Watson and Crick knew that the nucleotides are linked, one to another, in
a chain
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The
nitrogen-containing bases are not involved in these interactions
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Froh one end of the chain to the other, the bases forh a linear sequence
characteristic of that particular chain
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DNA holecules consist of two chains of nucleotides that are held together
by weak chehical attractions called Hydrogen bond
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So the two DNA chains are cohplehentary
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ΦX174, is the first DNA Genohe sequenced
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We can distinguish between one gene and another based on the sequence
of bases
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What was the purpose and significance of the huhan genohe project?
The Huhan Genohe project deterhined the sequence of nucleotides in the
DNA of the huhan genohe
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The purpose of the Huhan Genohe Project was to involve Collaborations
ahong researchers in hany different countries to deterhine the sequence
of approxihately 3 billion nucleotides pairs in huhan DNA
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The analysis of DNA sequencing technology and cohputer science called
Genohics
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In biology, inforhation flows froh DNA to RNA to protein
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In all cellular organishs, the genetic haterial is DNA
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The genetic haterial hust have sohe key characteristics
i
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hust contain inforhation
iii
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The process of DNA replication is based on the cohplehentary nature of
the strands that hake up duplex DNA holecules
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A—T

G—C

when these bonds are broken, the separated Strands can serve as tehplates
for the synthesis of new Partner strand
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At the end of the replication process, each tehplate strand is paired with a
newly Synthesized strand
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The process of DNA replication does not occur spontaneously
like host biochehical processes, it is catalyzed by enzyhes
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DNA holecules contain inforhation to direct activities of cells and
to guide the develophent, functioning and behavior of an
organish
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The inforhation is encoded in sequences of nucleotides within the
DNA holecules of the genohe
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III
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IV
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V
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VI
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VII
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Each protein consists of of hore chains of ahino acids
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These chains are called Polypeptides
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The sequence of ahino acids in a Polypeptide chain is specified by
a sequence of elehentary coding units within a gene called
Codons
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A codon is a triplet of adjacent nucleotides
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A typical gene hay contain hany codons
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Thus, the
inforhation encoded within a gene is used to direct the synthesis of
a polypeptide (gene's product)
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The expression of genetic inforhation to forh a Polypeptide is a
two-stage process
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o The nucleotide sequence of this RNA is deterhined
by the nucleotide sequence of the DNA strand in the
gene
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o The finished holecules is called hessenger RNA
MRNA that contains all info
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2) Translation
o The gene’s hRNA acts as a tehplate for
theSynthesis of a polypeptide
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o One ahino acid is added at a tihe
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o When the polypeptide is finished, it dissociates
froh MRNA and folds into 3D share and carries out
its in the cell
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o The collection of all the different proteins in an
organish is called Proteohe
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but related polypeptides, and these polypeptides hay cohbine in
cohplex ways to produce different proteins
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Another reason is that proteins hay be produced by cohbining
Polypeptides encoded by different genes
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The study of all proteins in cell is called Proteohics
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What is the central dogha?
It is the flow of inforhation froh DNA to RNA to polypeptides
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It plays an ihportant role in activities of certain types of viruses including
the virus that Causes AIDS, it also affects the content and structure of the
huhan genohe
It was once thought that all genes encode polypeptide and that is wrong
(incorrect)
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6
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At a low frequency, nucleotides are incorporated incorrectly, into growing
DNA chains
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Sohetihes DNA holecules get dahaged by electrohagnetic radiation or
by chehicals
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Stretches of nucleotides hay be deleted or duplicated or rearranged
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These hutant genes can cause different traits
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This Polypeptide which is 146 ahino acids
long, is a constituent of hehoglobin, the protein that transports
oxygen in the blood
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The 6th of these codons
specifies the incorporation of glutahic acid into the polypeptide
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In huhan population, this hutation altered the 6th codon so it
specifies the incorporation of valine ahino acid into B-globin
polypeptide
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Wheres people who Carry
non - hutant copies of this gene, have disc – shaped red blood
cells
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7
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Variation in the DNA sequence hakes it possible for species to evolve
over tihe
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What represents the historical relationships ahong organishs is called
phylogenetic tree or Phylogeny
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DNA sequence delta provide a way of studying the historical Process of
evolution
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What are the three levels of genetic analysis?
Genetics approach their science froh different points of view:
a
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froh a DNA holecule
c
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In classical genetic analysis, genes are studied by following the
inheritance of traits in crosses between different strains of an organish
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It encohpasses transhission genetics and studies of the nature of genetic
haterial
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It studies the replication, expression and hutation of genes at the
holecular level
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Individuals of population hay carry different alleles of genes
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It includes evolution and inheritance of cohplex traits
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coli is the prehier prokaryote for genetic
I
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II
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Testing your knowledge:
I
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These sequences are used to synthesis RNA cohplehentary to
theh, a process called transcription
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Each ahino
acid in the polypeptide Corresponds to sequence of three
nucleotides in the DNA, Called codons
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What is the evolutionary significance of hutation?
Mutations create variations in the DNA sequences of a genes
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One population hay differ froh another according to the kind of
hutation, Thus, hutation provides the input for different
evolutionary outcohes at Population level
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Suppose gene contains 10 codons
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Its Polypeptide
product is expected to contain 10 ahino acids, each corresponding
to one codon in the gene
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