Impact of Genetics on Human Affairs

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• Impact of Genetics on Human Affairs
• Application of genetic principals allowed for
  development of civilization
• - selection of plants and animals for
• domestication
• Expansion of agricultural production
• green revolution- application of Mendelian
  principals of hybridization and trait selection-
  superior varieties of wheat, rice corn
• - herbicide resistance, golden rice (essential
  amino acid), pest resistant (Bt Corn)
• genetically modified bacteria, plants and
  animals- express proteins of agricultural and
  medical importance
• recombinant vaccines, insulin production ,
  human growth hormones
• Antibiotics and other pharmaceuticals

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• Human medical diagnostics
• - identification and screening of genetic
  defects-
• prenatal diagnosis and screening for
  heterozygous carriers of recessive eg. sickle
  cell anemia, cystic fibrosis, Tay-Sachs disease
• - determination of molecular causes of
  diseases-remedial medicine
• - gene therapy used to transfer genes with
  normal activity to replace the mutants viral
  vectors are used
• Human genome project and ethical issues

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• What is genetic material?
• Except in certain viruses, DNA is the genetic
  material in all living organisms.
• Is organized into structures called chromosomes.
  Consist of principally deoxyribonucleic acid
  (DNA) and proteins
• Prokaryotes The genetic material usually consist
  of a single nucleic acid molecule which is often
  a circular strand.
•  Eukaryotes true nucleus genetic material is
  arranged into multiple chromosomes and divided by
  mitosis.
•  Chromosome complement
• The number of copies of the genetic material
  within a cell is known as the ploidy level.

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• Most Eukaryotes are diploid (2n) (2 copies each
  chromosomes per parent)
• Most Eukaryote gametes are haploid (n) Only one
  set of chromosomes per parent.
• Ex Humans 2n46
• Fruitfly 2n 8
• In diploids chromosomes exist in pairs-each pair
  is called homologous chromosomes with each
  individual member of the pair called a homolog
• Homologous chromosomes similar in size,
  structure and gene arrangement.
• Homologous chromosomes contain identical gene
  sites along the lengths each called a locus
  (pl.loci)
• In a pop. members of the same species can have
  many different forms of a same gene, called
  alleles.
• .

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• Human females XX-homologous Males XY-
  non homologous
• Each diploid organism contains two copies of a
  gene along the length of a chromosome- due to
  biparental inheritance.
• Chromosome structure- distinctive lengths and
  shapes contains a condensed or constricted
  region called the centromere
•  

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• Chromosomes other than sex chromosomes are called
  autosoms
•  chromosome structure
• Metacentric, submetacentric, acrocentric or
  telocentric.
• The shorter arm, p arm and the longer q arm

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• Structure of genetic material - Before the
  nature of DNA and RNA was known it was clear that
  the genetic material had to have 4 principal
  features.
• (a) It must contain inforn for the cell to
  survive-repository of information most cells
  have a complete complement but might express only
  some at a certain point in time
• (b) It must replicate
• ( c ) It must be capable of expressing the
  information- process of information flow- how DNA
  makes RNA and RNA makes protein is known as the
  central dogma of molecular genetics
• (d) Must be capable of generating variation by
  mutation- a change in the DNA sequence would
  reflect in the transcription and translation and
  finally affect the protein produced

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• The genetic Material early studies
• DNA was first studied in 1868 by a Swiss chemist
  Friedrick Miescher, isolated cell nuclei and
  derived an acid substance containing DNA which
  was called as nuclein this lacked the
  chemical diversity to store inforn-. Levenes
  observations in 1910 said that DNA contained
  equal amounts of 4 quite similar molecules called
  nucleotides and these 4 components were
  repeated over and over - Levene postulated
  incorrectly the tetranucleotide hypothesis,
  thought the structure would be similar to
  proteins, in 1940 Erwin Chargaff showed that most
  organisms do not contain equal proportions of the
  4 nucleotides.

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• By this time researchers knew that genetic
  material was either protein or DNA though the
  structure and the exact material was yet to be
  determined.
• Transformation studies Fredrick Griffiths
  (1927) Injected mice with different strains of
  the bacteria (Diplococus pneumoniae)
• Virulant strain smooth (s) due to the
  polysaccharide capsule
• Avirulant strain rough ( r )
• Living virulant cells-produce pneumonia
• Heat killed virulant bacteria- no infection
  similar to living to avirulant

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• Griffiths critical experiment-
• Living IIR cells heat killed IIIS
  mouse lives and living IIIS cells were recovered
• Griffiths concluded that the heat killed IIIS
  bacteria converted live avirulant IIR cells into
  virulent IIIS cells
• he called this phenomenon, transformation and
  suggested that the transforming principle might
  be some part of the polysaccharide capsule or
  some compound required for capsule synthesis

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• In 1944, Avery, MacLeod and McCarty reported
  that the transforming principle was DNA, Fig
  10-3,
• they further showed that once transformation
  occurs the capsular polysc. Is produced in
  successive generations and is heritable the
  process affects the genetic material- classical
  paper in molecular genetics
• The second major piece of evidence supporting DNA
  as the genetic material was provided by Alfred
  Hershey and Martha Chase (1952).
• They used the bacterium E.coli and and one of its
  infecting viruses bacteriophage T2 (phage)
  virus consist of a protein coat DNA (hexagonal
  head and the tail)

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• at the infection, the phage adsorbes to the
  bacterial cell and the components of the phage
  enters the bacterial cell, the viral information
  then is reproduced by the host mechanisms and
  virus undergoes reproduction. Many new phages are
  constructed and the bacterial cell is lysed
  releasing the progeny viruses

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• .
• Harshey and Chase knew that phage contains 50
  protein 50 DNA, but what makes the viral
  reproduction?
• They used radioisotopes to follow the molecular
  components of phages during infection- Both P32
  and S35, radioactive forms were used.
• DNA contains P not S, then P32 labeles DNA and
  S35 labells proteins. Fig. 10-5

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• Harshy and Chase boiled this down to 2
  conclusions
• It was DNA and not protein that entered the
  bacterial cell that cause the infection
• DNA must be the material responsible for the
  function and reproduction of phage T2.
• Indirect and direct evidence that DNA is the
  genetic material
• Indirect The genetic material is found where it
  is functioned DNA is located almost exclusively
  in the nucleus of the cell and also in
  mitochondria and chloroplasts
• The amount of DNA and the of sets of
  chromosomes are directly correlated no
  consistant corrn can be observed between gametes
  and diploid cells for proteins

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• Direct Recombinant DNA studies segments of DNA
  corresponding to specific genes are isolated and
  spliced into bacterial cells where they are
  expressed in the bacteria ex. Human insulin and
  interferon are produced by bacteria
• In some viruses RNA is the genetic material
• Ex. Tobacco mosaic virus
• Purified RNA of Tobacco mosaic virus is spread on
  tobacco leaves the characteristic lesions
  appeared- concluded that RNA is the genetic
  material in these viruses
• RNA can be replicated in vitro using enzyme RNA
  replicase isolated from host E. coli cells.
• Retroviruses- Their RNA serves as a template for
  the synthesis of the complimentary DNA molecule.
  The process called reverse transcription occurs
  under the direction of DNA polymerase enzyme
  called reverse transcriptase.
• ex. HIV which causes AIDS as well as RNA tumor
  viruses

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• Nucleic acid chemistry
• DNA is a nucleic acid, and nucleotides are the
  building blocks. A nucleotide consist of 3
  essential components a nitrogenous base, a
  pentose sugar and a PO4 group. There are two
  kinds of nitrogenous bases
• Purine ring
  Pyrimidine ring
• Adenine, Guanine
  Cytosine, Thymine
• 
  and Uracil

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• Both DNA and RNA contain adenine, cytosine and
  guanine, and only DNA contains thymine and only
  RNA contains uracil.
• The pentose sugars in nucleic acids give them the
  name, Ribonucleic acid (RNA) contain ribose (C2
  has a OH )while deoxyribonucleic acid (DNA)
  contain deoxyribose (C2 has a H )
• Ribose sugar

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• 5 PO4 end and 3
• OH end
• Base sugar nucleoside
• Base sugar PO4 nucleotide
• Phosphodiester bond, each bond is between 3 and
  5
• The addition of PO4 groups to the C5 is named as
  two PO4 named as diphosphates and 3 PO4
  triphosphates

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• Structural analysis of DNA in 1953 James Watson
  and Francis Crick working in the Cavendish
  Laboratory in Cambridge UK proposed that the
  structure of DNA is in the form of a double
  helix.
• The evidence they had at the time
• Bases, sugars and PO43- gps all linked to a
  polynucleotide chain.
• Erwin Chargaffs rules that AT GC (amount of
  purines are equal to amonut of pirimidines A
  always binds to T and C always binds to G,
  complementarity)
• Roslind Franklin and Maurice Wilkins had shown
  using X ray diffraction that the molecule has a
  helical structure
• Watson and Crick used this inforn and build a 3
  dimensional model for the structure of DNA
• DNA consist of 2 chains of in a right hand double
  helix,.
• The diameter is 2 nm the two chains are
  antiparallel (opposite polarity 5-3 and 3-5)
• The sugar phosphate back bone is on the outside
  and the bases are on inside

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• Both DNA and RNA are assembled from nucleoside
  triphosphates.
• For DNA, these are dATP, dCTP, dGTP, and dTTP.
• For RNA, these are ATP, CTP, GTP, and UTP.
• In both cases, as each nucleotide is attached,
  the second and third phosphates are removed.
• The nucleosides and their mono-, di-, and
  triphosphates
• Base Nucleoside
  Nucleotides
• DNA Adenine (A) Deoxyadenosine dAMP dADP
  dATP
• Guanine (G) Deoxyguanosine dGMP
  dGDP dGTP
• Cytosine (C Deoxycytidine dCMP
  dCDP dCTP
• Thymine (T) Deoxythymidine dTMP
  dTDP dTTP
• RNA Adenine (A) Adenosine AMP
  ADP ATP
• Guanine (G) Guanosine
  GMP GDP GTP
• Cytosine (C) Cytidine
  CMP CDP CTP
• Uracil (U) Uridine
  UMP UDP UTP

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• The bases are held together across the two
  strands by weak H bonds C paired with G 3 H
  bonds (C---_G) A paired with T 2 H bonds (AT).
  Each complete turn of the helix is 34A0 (3.4nm)
  long thus, 10 bases exist per turn in each turn
• The double helix measure 20 A0 (2.0nm) in width
• They pursued the idea of the structure of DNA
  further and suggested a specific mode of
  replication of DNA- the semiconservative model.
• Two new concepts were put forward the storage of
  genetic information in the sequence of the bases
  and the mutations or genetic changes that would
  result from an alteration of the bases.
• Alternative forms of DNA Under different
  conditions of isolation several conformational
  forms of DNA has been recognized. At first only A
  B forms were known.

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• A form-prevalent under high salt or dehydration
  conditions. It is more compact with 11bp in each
  complete turn of the helix. A right handed helix.
• Z form Contains only C-G pairs, a left handed
  double helix and 18 nm in diameter, 12 bp per
  turn and assumes zizag conformation , it is not
  clear whether Z DNA occurs in vivo
• Structure of RNA In RNA, the sugar is ribose
  and nitrogenous base thymine of DNA is replaced
  by Uracil. Most RNA is single stranded, but with
  two exceptions RNA molecules sometimes fold back
  on themselves to form complementary base pairs,
  some animal viruses that have RNA as genetic
  material contain double stranded helices.

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• Three major classes of cellualar RNA molecules
  function during the expression of genetic
  information ribosomal RNA, messenger RNA and
  transfer RNA . All these originate as
  complementary copies of one of the two strands of
  DNA segments during the process of transcription
  I.e. it uses the DNA strand as the template
• In addition there are small nuclear RNA (SnRNA)
  participate in processing mRNA, Telomerase RNA-
  is involved in DNA replication at the ends of
  chromosomes and antisense RNA involved in gene
  regulation.
• DNA storing genetic information
• RNA function in the expression of information

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• Characteristics of DNA Because of the presence
  of H bonds DNA has special qualities, If DNA is
  isolated and subjected to slow heating the double
  helix is denatured and unwinds if a mixture of
  single strands that are complementary to each
  other are slowly cooled they will reassociate
  re-forming the helix.
• In a melting profile of DNA, (where OD 260 is
  plotted against temp, the midpoint of each curve
  is called the melting temp.Tm 50 of strands are
  unwound. (the GC rich DNA has high Tm)
• OD 260 absorption of UV light by a DNA
  molecule is related to the viscosity of DNA such
  that when heated DNA unwinds and during unwinding
  viscosity decreases and UV absorption increases.
• The property of denaturation/renaturation of
  nucleic acids is the basis for one of the most
  powerful and useful techniques molecular
  hybridization If a reasonable degree of base
  complementarity exist under proper temp.
  conditions two nucleic acid strands from
  different sources will rejoin, DNA and DNA or
  DNA/RNA

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• This technique has been useful to target DNA of
  cells by hybrid formation. The process is known
  as in situ molecular hybridisation. Mitotic or
  interphase cells are fixed to slides and then
  subjected to hybridisation using single strandard
  DNA which are radioactive or contain a
  fluorescent label. This technique using the
  fluorescence is known as FISH (fluorescent in
  situ hybridisation)
• Repititive DNA copies present many times in the
  genome and is prevalent in the eukaryotic
  genomes. There can be short DNA sequences
  repeated over a million times.
• Electrophoresis of nucleic acids
• Separation of different sized DNA or RNA on a
  semi solid base under the influence of an
  electric field is known as electrophoresis. The
  basis is if two molecules have app. The same
  shape and mass the one with the greatest net
  charge migrates more rapidly towards the
  electrode of opposite polarity.