Human Genetics

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Unit 4

• Human Genetics Biotechnology

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Control of Gene Expression in Prokaryotes

• What is a prokaryote?
• If they have no nucleus, where is their DNA?
• Plasmid ring of bacterial DNA

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Lac Operon

• What is lactose where do we find it?
• Carbohydrate, disaccharide, glucose galactose
  dairy
• What is lactase?
• An enzyme that breaks down lactose
• What is an enzyme?
• A protein catalyst that speeds up a rxn. by
  lowering activation energy is not consumed in
  the rxn.
• When would a bacterium want to make lactase?

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Repression

• Regulatory gene (lac I), transcribed translated
  into repressor protein.
• Repressor binds to the operator (O) blocks RNA
  polymerase from transcribing the strucural gene
  for lactase (lac Z, lac Y lac A)

Lactose is absent
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Activation

• Lactose binds to repressor changing its shape
• Repressor cant bind to operator
• RNA polymerase proceeds to transcribe lactase
  is made

Lactose is present
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How is this like an on/off switch?

• When lactose is present, lactase is made.
• Once lactase breaks down the lactose, the
  repressor binds to the operator blocking
  transcription.
• Lactase is no longer made.
• This is efficient and is called regulation.

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Activation Repression
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Activation Repression
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Cell Differentiation

•       Most eukaryotes are multicellular
•       All of their cells contain identical genes
• The genes of a cell are turned on or off
  according to the specialized task of that cell

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• Fertilization
• Sperm Egg Zygote
• Cleavage
• Zygote Mitosis
• 2 identical cells
• 2 identical cells Mitosis
• 4 identical cells
• 4 identical cells Mitosis
• 8 identical cells
• . . . Etc.

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Cleavage

• occurs rapidly, not allowing the cells to grow
  before dividing ? ? the S.A./V

• Result is a ball of identical cells (looks like a
  golf ball) called a Blastula

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• At some point during the blastula stage of
  development the growing organism begins to take
  form, Morphogenesis.

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• Homeotic Genes (regulatory genes), determine
  where certain anatomical structures will develop
  during morphogenesis

• Homeotic genes translate into regulatory proteins
  which turn genes on or off

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• Each homeotic gene contains a sequence of 180
  bases, the homeobox, which regulates patterns of
  development

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? ? ? ? ? ? ? ? ? ? ? ? ?

• Scientists have found many different organisms
  with similar homeoboxes, this may be additional
  evidence for evolution

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CANCER

•   Uncontrolled, abnormal cell division
•   Normal cells will not divide if
• -    not enough energy
• -    not attached to fibers, membrane or other
  cells
• - too tightly packed together

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•   Cancer cells proliferate regardless of these
  factors, forming TUMORS
• - BENIGN (good) cells in tumor remain in a
  mass examples warts or fibroid cysts
• - MALIGNANT (bad) cells leave mass, invade
  destroy healthy tissues

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• METASTASIS spread of cancer cells from original
  site

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Types of Cancer categorized according to the
type of tissues they affect

• Carcinomas skin tissues that line organs (lung
  breast cancers)
• Sarcomas bone muscle tissue
• Lymphomas solid tumors in tissue that forms
  blood cells (leukemia uncontrolled WBCs)

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Causes of Cancer

• Heredity
• Mutations
• Carcinogens

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Sex Determination

• Determined by the sex chromosomes, X Y
• Question Chromosomes not involved in sex
  determination are called ____?_____
• Answer Autosomes

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(No Transcript)
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• What are the chances of having a boy or a girl
  baby?
• 49 Girl
• 51 Boy
• (106 boys to 100 girls on average)

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Why?

• Y chromosome weighs less than the X ? sperm
  carrying the Y are lighter can travel faster
  further than the X sperm

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Sex Linked Traits

• Traits determined by genes carried on the sex
  chromosomes
• Most are found on the X chromosome because there
  is more space than on the Y

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ExamplesEye Color in Drosophila melanogaster
(fruit fly studied bygeneticist Thomas Hunt
Morgan in early 1900s)

•       Sex linked dominant

  R red eyes r white eyes
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Hemophilia in Humans
Sex linked recessiveh hemophilia
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What is the probability that a carrier female and
a normal male will pass hemophilia to their son?
Daughter? (Use a Punnett Square to explain your
answer.)
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50 probability of passing to son0 probability
of passing to daughter
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Mutations

• Change in DNA
• Germ cell (creates sex cells) mutation does not
  affect the individual, but does affect the
  offspring
• Somatic cell (autosome) mutation affects the
  individual and not the offspring

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Chromosome Mutations

• 1) Deletion-
• loss of a piece of a chromosome

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• 2) Inversion-
• piece breaks off reattaches to the same
  chromosome in the reverse direction

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• 3) Translocation-
• piece breaks off reattaches to a non-homologous
  chromosome

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• 4) Non-Disjunction-
• when a replicated pair of chromosomes fail to
  separate

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Gene Mutations/Point Mutations

• substitution, addition, or deletion of a single
  nitrogen base

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Substitution

• ?
• A A
• C T
• T T
• G G
• A A
• A A

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Deletion

• ?
• C C
• C C
• T T
• T T
• G G
• G G
• A __
•  

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Addition

• ?
• C C
• T T
• T T
• G G
• A A
• C A
• T C
• G T
• G

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• NOTE Deletions or additions result in a frame
  shift mutation that effects all amino acids
  following the mutation.

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Human Genetics

• Traits, Diseases, Disorders, Detection
• (Me my sister, Jess, at the Getty Museum)

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1. Sickle Cell Anemia

•   Point Mutation
•   Codominance
•  
• AA normal RBC
• AA sickle-shaped RBC
• AA some normal some partially sickle-shaped

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2. Huntingtons Disease

• Single allele trait
• Dominance
• Genetic Marker section of DNA associated with
  HD has been identified

• Symptoms
• appears in 30s or 40s
• forgetfulness
• irritability
• loss of muscle control
• uncontrollable spasms
• death

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3. Polygenic Traits

• traits controlled by 2 or more genes
• examples skin, eye, hair color

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4. Multiple Alleles

• a trait controlled by 3 or more alleles

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Example Blood Type

• Alleles
• IA
• IB
• io or i
• A B are codominant
• A B are dominant over O

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What phenotypes correspond to each genotype?
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5. Sex Influenced

• a trait that is influenced by the presence of
  male or female hormones

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Example Baldness

• B dominant in males, recessive in females
• B will not lose hair
• Male BB
• Female BB
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• Male BB ? bald
• Female BB ? not bald
•  
• Male BB
• Female BB

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6. Non-disjunction

• failure of chromatids to separate during meiosis

Normal Meiosis
Non-Disjunction
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Results
Monosomy
Trisomy
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Types of Non-disjunction Mutations
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1.  Trisomy 21 or Down Syndrome

• three 21 chromosomes, resulting in mental
  retardation with weak muscles

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2. Turner Syndrome

• Female, with external internal genetalia,
  except no ovaries

X
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3. Kleinfelter Syndrome

• Male, small testes, low sperm count, little body
  hair

XXY

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Detecting Human Genetic Disorders

• A. Genetic Screening
•  
• B. Genetic Counseling
•  
• C. Ultrasound

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D. Amniocentesis

• Sample of fetal cells from amniotic fluid is
  extracted by a needle inserted into the womb

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E. Chorion villi Sampling (CVS)

• Tissue sample between the uterus placenta is
  taken
• Can be performed earlier than amniocentesis

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Genetic Engineering

•  Application of molecular genetics for practical
  purposes
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• Can be used to
• -  Identify genes for specific traits
• -   Transfer genes from one organism to another
• -    Cure diseases
• -    Treat disorders
• -   Improve crops

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Manipulating Genes
     

• Restriction Enzymes
• Bacterial enzymes used to cut DNA molecules into
  manageable pieces
• These enzymes recognize specific sequences of
  nucleotides

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Example

• Enzyme recognizes a specific sequence of DNA
  running in both directions
• Enzyme cuts btwn. the G A on each strand
  leaving single chain tails called sticky ends

C T T A A / G G / A A T T C
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Cloning

• Cloning vector transfers the gene isolated by the
  restriction enzyme to another organism
• Bacteria contains a cloning vector called a
  plasmid, a circular ring of DNA

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Procedure

• Plasmid is removed from bacterium
• Plasmid is cut using same restriction enzyme
  donor gene is inserted
• As the bacteria divides, gene is replicated, thus
  cloning the gene
• Gene clone is an exact copy of the gene
• Transgenic organism, bacterium containing the
  gene clone can be used to infect other organisms

Try this site for more information diagrams!
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Practical Uses

• A transferred gene is transcribed translated as
  though it were in its normal cell
• Human insulin can be isolated reinserted into
  bacterial DNA to make recombinant DNA
• Learn about Gene Therapy

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DNA Technology

• DNA Fingerprint

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What is it?

• Pattern of bands made up of specific fragments
  from an individuals DNA

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What does it look like?

• Appear as fuzzy bands made up of stain arranged
  in columns

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What is it used for?

• Can be used for comparisons to see if people are
  related (paternity tests) for forensics (crime
  science)

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How is it made?
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1. RFLP (Restriction Fragment Length
Polymorphism) Analysis

• Extracting DNA from specimen
• cutting it using restriction enzymes

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2. Gel Electrophoresis

• Cut DNA is placed in wells of gel electric
  current is run through the gel
• DNA is (-) migrates towards ()
• Fragments separate based on size (larger, migrate
  slower)

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3. Probes

• Radioactive segments of DNA complementary to the
  segments being compared
• Allow the fragments to be visualized
  photographed for analysis

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How accurate is it?

• Only identical twins share the same set of DNA
• But only a small portion of a persons DNA is
  being compared in a fingerprint

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What if the sample is too small?

• A Polymerase Chain Reaction (PCR) can be used
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• Used to multiply a DNA sample when it is too
  small to be analyzed
•  
• DNA nucleotides, DNA polymerase primers
  (artificial single stranded DNA) when combined
  heated will reproduce