GENETICS

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GENETICS
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What is Genetics?

• The Study of similarities and differences between
• relatives.

What is it that elephants have that no
other animal has?
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What is Genetics?

• The study of similarities and differences
  between
• relatives.

What is it that elephants have that no
other animal has?
Baby Elephants!
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Why do we resemble our parents?

• Our parents provided most of the information (in
  the sex cells) that governs our appearance, our
  activity, and our behavior.
• They provided most of the GENES.
• Genetics is also seen as the study of Genes or
  genetic variation.

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Genetics Attempts to Answer These Questions

• 1. How are Genes Transmitted?
• 2. What are Genes?
• 3. How are Genes (the genetic material)
  organized to function efficiently?
• 4. What kind of activities do Genes control?
• 5. How do Genes control these activities to
• produce the differences we see?

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Early ideas about inheritance

• Archeological evidence from 8,000 1,000 B.C.
  shows horses, camels, and oxen had been
  domesticated and that various breeds of dogs had
  derived from wolves, through artificial
  selection.

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Early ideas about inheritance

• Cultivation of many plants, including wheat, corn
  and rice as well as the date palm began as early
  as 5,000 B.C.
• The appearance of new varieties from unconscious
  attempts to breed and cultivate must surely have
  led in time to conscious attempts to propagate
  desirable traits and the elimination of
  undesirable traits by the breeders.

wheat
corn
corn
Rice
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Early ideas about inheritance

• The Assyrians were sophisticated and experienced
  breeders of domesticated plants and animals and
  had artificially pollinated date palms (shown at
  right) by 800 B.C.

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Simple rule of heredity

• These early practitioners seemed to work from the
  simple rule of heredity like breeds like and
  sometimes unlike!
• Select breeds with the desirable characteristics
  and breed them!

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The Greek Influence on ideas of inheritance

• Hippocrates Humors, which could be altered
  during an individuals lifetime and therefore
  diseased or normal, were drawn from various parts
  of the body to the semen and passed on to the
  offspring. This pangenesis theory even formed
  the basis of Darwins early ideas of inheritance.
  
• Aristotle semen produced a vital heat that
  cooked and shaped the menstrual blood giving it
  the capacity to produce offspring with the same
  form as the parent.

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Later ideas of inheritance (1600- 1850)

• Pre-formationism sex cells contain a complete
  miniature adult (the homunculus) ?
• Epigenesis presumably put forth by Harvey, held
  that body structures were not present in the sex
  cells, but were formed anew.

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Other ideas of inheritance

• Pangenesis the inheritance of acquired
  characteristics put forward again by Jean
  Baptiste Lamarck.
• the notion was discredited by August Weissman,
  who cut tails off mice for 22 generations and
  continued to get mice with long tails
• Blending Inheritance the belief that
  characteristics of parents blended like paint,
  e.g., mix blue and yellow and get green paint.

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Gregor Mendel

• Seven years after Darwin published his theory,
  Mendel, an Austrian monk, published (in 1866)
  his findings on inheritance in peas. Mendel
  discovered the rules governing vertical gene
  transmission.

Gregor Mendel
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Mendels Discoveries (2 laws)

• Mendels 1st Law - The Law of Segregation
  (essentially has 4 parts)
• 1. Alternative versions of genes account for
  variations in inherited characters.

In a simple case, shown here are 2 versions of a
gene. Where the flower of the pea plant is
yellow (due to gene y) or purple (due to gene Y).
Many genes have hundreds of alternatives, and
might be expressed thus Y1, or Y2, or Y3, or Y4,
orY5, etc.
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Mendels 1st law (parts 2 and 3)

• 2. For each character, an organism inherits 2
  genes, one from each parent.
• 3. If the 2 genes differ, then one, the
  dominant gene, is expressed and the other, the
  recessive gene has no noticeable effect on the
  organisms appearance.

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Mendels 1st law (part 4)

• 4. The 2 genes then separate again when the
  organisms forms sex cells (gametes), each sex
  cell receiving only 1 of the 2 possible genes.

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Mendels Discoveries (the 2nd law)

• Law of Independent Assortment.
• The most important principle of this law is that
  the emergence of one trait (e.g., plant height)
  will not effect the emergence of another (e.g.,
  flower color)

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New Offspring New gene combinations

• Built into the mechanism for gene transmission is
  a means for creating variability. Reshuffling of
  genes in the sex cells of the parents creates new
  combinations of genes in the offspring.
• Totally new genes can be created by Mutation.

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Highlights of some discoveries following Mendels
work

• 1900 - Mendels work was rediscovered.
• 1902 - Sutton proposed that genes were located
  on chromosomes.
• 1944 - The genetic material was found to be DNA.
• 1953 - Watson and Crick propose a model for the
  structure of DNA that also suggests a
  means for its faithful replication.
• 1966 - How DNA worked to control the activities
  of the cell had all been worked out
  DNA ? RNA ? protein

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Highlights of some discoveries following Mendels
work (cont.)

• 1973 Recombinant DNA molecules formed.
• 1977 Sequencing of DNA achieved.
• 1983 PCR technique developed.
• 1990 First successful gene therapy.
• 1995 The Human Genome Project (HGP)
  gets underway.
• 2003 HGP essentially completed.

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Vertical Gene Transmission

• While most of our genes come from our parents
  (vertical transmission) some may not have!!!
• Some of it is coming in horizontally. It seems
  that some of our genetic material is coming from
  viruses and other parasites that invade us.

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Horizontal Gene Transmission

• The Human Genome Project (HGP) has found that
  there is a lot of the DNA of our genes that is
  identical to that of viruses.
• These parasites have the ability to introduce
  some of their genetic material into their hosts
  (meaning us) genetic material.

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Horizontal Gene Transmission (HGT)

• These viruses have apparently been doing this for
  millions of years.
• These viral elements make up 45 of our DNA and
  fully 8 of that comes from retroviruses. HIV is
  a retrovirus.

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Horizontal Gene Transmission (HGT)

• What are these viral genetic elements doing in
  our DNA? Are they having any effect?
• The answer appears to be that they are having an
  effect.the complete answer remains to be
  discovered when more research is done.

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What are Genes?

• Genes consist of a polynucleotide chain called
  DNA (or RNA for some viruses) that generally
  exists as a double helix.

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What are Genes?

• The nitrogen bases, here represented with the
  letters A, T, G, and C, signify a code that is
  translated into one of the 20 amino acids that
  make up every protein found in every organism on
  earth.

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What are Genes?

• Each nitrogen base always pairs with another base
  such that A always pairs with T and G with C.
  There are 3,200,000,000 base pairs in each human
  cell, a string that would stretch 1 meter (ca. 3
  feet) in length.

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What are Genes?

• A gene is a string of nitrogen bases that
  dictates the manner by which Proteins are
  made.nothing more.nothing less.
• Proteins are made up of strings of amino acids.
  They function as enzymes (organic catalysts) and
  as structural building blocks of the cell.
• A gene, then, is a recipe for making a protein.

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How much DNA (or genes) do cells have?

• Species Genes DNA (bp)
• E. coli (bacterium) 4,400 4,600,000
• Yeast cell 6,000 12,000,000
• Roundworm 19,000 97,000,000
• Fruit fly 13,600 165,000,000
• Rice plant 55,000 466,000,000
• Gallus gallus (Chicken) 23,000
  1,000,000,000
• Rat 30,000 2,750,000,000
• Homo sapiens (human) 25,000
  3,200,000,000
• Amoeba proteus (amoeba) ?
  290,000,000,000

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How much DNA (or genes) do HUMAN cells need?

• First of all, if we assume 25,000 genes in the
  human, and use a figure of 3,000 bp per gene then
  we need only 75 million bp for all our genes. We
  have about 3.2 billion base pairs in our DNA!!
• This means we can account for all our genes with
  only 2 of the DNA in our cells.
• The rest is referred to as Junk or repetitive
  DNA.

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How is all this genetic material organized to
function efficiently?

• In diploid organisms like ourselves, the DNA is
  organized into chromosomes.

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What kinds of activities do genes control?

• Virtually every type of activity a cell or
  organism engages in is controlled by
  genesthrough the formation of proteins.
• There are 2 major types of proteins
• 1. Structural involved in building and
  maintaining subcellular structures.
• 2. Functional enzymes.

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How do genes control activities?

• Since proteins control essentially all the
  activities of a cell, if the cell knows how to
  make all the proteins.it doesnt need to do
  anything else.
• Enzymes carry out all the reactions in a cell.
• Structural proteins combine with other proteins,
  carbohydrates and lipids by a process known as
  self-assembly to form all the sub-cellular
  structures within the cell.

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We know exactly how the cell does this
DNA in the nucleus of the cell makes a nearly
identical copy of itself and transports this
copy to the site of protein synthesis in the
cell. Using the genetic code, the message
originally present in the DNA and transcribed
into the RNA copy is translated into a protein.
This process takes only seconds to accomplish
since it is aided by enzymes.
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Cells translate the message in the genetic code
to create proteins.

• The 4 bases in the DNA are a recipe for adding
  amino acids one by one to make a protein, and 61
  of the 64 possible ways of arranging these 4
  bases in 3-letter words proscribes an amino acid.
  The remaining 3 order a STOP to the process.the
  protein is done.

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We differ from our parents because the proteins
coded from DNA are different!

• Individuals differ from one another in the
  specific sequence of bases in their DNA.
• 1TAGGCTGGCATTATATGCGAATTG
• ATCCGACCGTAATATACGCTTAAC
• 2TAGGCTGGCGTTATATGCGAATTG
• ATCCGACCGCAATATACGCTTAAC

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Changes in DNA ultimately result in changes in
the amino acid (message)

• TAGGCTGGCATTATATGCGAATTG
• THE CAT SAW THE RAT
• ..TAGGCTGGCGTTATATGCGAATTG
• THE CAT ATE THE RAT

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The HUMAN GENOME PROJECT

• We have just completed sequencing the entire
  human genome and there are exactly 3.164 billion
  base pairs in the human genome.
• The best estimate is that there are only 25,000
  genes, half of which we dont yet know the
  function.
• The rest consists of highly repetitive sequences
  (e.g., TTTGGCTTTGGCTTTGGC) repeated over and over
  thousands of times.

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The HUMAN GENOME PROJECT

• Almost 99.9 of the base pairs are exactly the
  same in all people! (This still leaves about 3
  million base pairs that differ among any two
  individuals) Focus on the similarities
• The genome is full of non-coding or Junk or
  repetitive DNA but even this can be useful for
  DNA Fingerprinting.

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DNA Fingerprinting

• Can help to convict the guilty and exonerate the
  innocent.
• In a famous case in England, a rapist was caught
  3 yrs after the crime when DNA from the sperm was
  matched with his DNA.

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What can we do with all that we have learned
about genes?

• The first organism to have its genetic material
  completely sequenced was a bacterial virus
  (FX174). It has 5,386 base pairs. Using this
  information, researchers 2 years ago synthesized
  a completely artificial virus from lab chemicals
  that was 100 identical to the natural FX174
  virus and it was able to behave like the natural
  virus infecting a bacterial cell. We have
  created life in a test tube or at
  least..duplicated it!

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What else can we do with what we have learned
about genes?

• We can isolate individual genes from any organism
  or individual.
• We can make millions of copies of that gene in a
  matter of hours.
• We can combine that gene with others in what is
  called a Recombinant DNA molecule and insert that
  into most any organism we choose. This is called
  Genetic Engineering

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Genetic Engineering
Human insulin produced in a bacterium using
a gene obtained from humans.
Bacterium full of insulin
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Gene Therapy

• The technology may eventually be used to treat a
  whole range of inherited disorders
• for example, why not introduce the gene for
  insulin production into insulin-dependent
  diabetics rather than having them rely on
  frequent insulin injections?

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Gene Therapy (cont.)

• SCID (severe combined immunodeficiency disease)
  is a fatal condition due to the absence of an
  enzyme, adenine deaminase or ADA.
• Individuals with this disease lack a functional
  immune system. They must be kept in a sterile
  environment. They were often referred to as
  bubble babies.

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Gene Therapy (cont.)

• The gene for ADA has been isolated, combined with
  a harmless virus (Recombinant DNA) and introduced
  into children with this condition. The photo on
  the right shows one successful application of
  this technology.

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Gene Therapy (cont.)

• Of course, every new technology has its downside
• Performance-enhancing drug use has become a big
  problem in both professional and amateur
  athletics. Periodic testing for these drugs
  probably reduces their use somewhat.

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Gene Therapy (cont.)

• What if athletes began to use gene doping,
  where genes for Human Growth Hormone (HGH) or
  Insulin-like Growth factor (IGF-1) would be
  introduced into their muscles? It would be more
  effective and essentially non-detectable.
  Olympic officials are definitely worried about
  this happening fearing it has the potential to
  ruin athletic competition as we know it.

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Gene Engineering

• A gene for insect resistance (Bt) has been
  engineered into most all of the corn we consume,
  rendering it quite resistant to the European corn
  borer.
• Many other fruits and vegetables have been
  engineered for drought and cold resistance and
  resistance to plant diseases.

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GENETICS

• The End