Gene Expressions in Humans: Chapter 11

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Gene Expressions in HumansChapter 11
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Intermediate Expression

• Blending or Incomplete Dominance
• Josef Kolreuter in 1760. Worked with carnations
• Crossed Red carnations with White
  carnations.
• He expected to get Red carnations.
• WRONG!!!
• Ended up getting all Pink carnations.

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How did this happen?

• P1 Red carnations (rr) x White carnations
  (ww)
• F1 Pink carnations (rw)
• F1 Pink carnation (rw) x Pink
  carnation (rw)
• F2 25 Red (rr) 50 Pink (rw) 25
  White (ww)
• 121 phenotype
  ratio!!
• 121 genotype ratio!!

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Incomplete Dominance or Intermediate Expression

• Hair color
• Eye color
• Height
• Face shape
• Wavy hair
• Pitch of males voice (tt tenor, tb baritones,
  bb low bass)
• Tay-Sachs Disease - inability to produce the
  enzyme hexosaminidase A.  Causes fluid pressure
  on brain then breakdown of brain. Starts a 6
  months w/ death by 2 3 years.  Most common
  among the descendents of Eastern European Jews
  (Ashkenazi Jews).
• Tt individuals produce 40-60 of enzyme

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Crosses

• 1. Cross a Round faced person with an oval faced
  person
• 2. Cross a Black with a white horse
• 3. Cross a Wavy haired person with a curly haired
  person
• 4. How could 2 brown eyed parents have a hazel
  eyed child?

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Codominance

• Condition in which both alleles of a gene are
  expressed or active
• Roan cattle or horses Red is codominant with
  white.
• Results in a Cattle or horse with some red and
  some white hair. (they look pink from a distance)
  Also a blue roan (black white hairs)
• Andalusian chickens have both
  black and white feathers.

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Roans
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Blood types in humans

• A is codominant with B resulting in AB blood

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Sickle Cell Anemia

• Discovered in 1904 by Dr. James Herrick
• Sickle Cell anemia gene is codominant to the
  normal red blood cell gene
• Normal red blood cells are round like doughnuts,
  move easily through small blood vessels
• Sickle red blood cells become hard, sticky and
  sickle shaped. When they go through small blood
  vessels, they clog the flow and break apart. This
  can cause pain, damage and a low blood count, or
  anemia.

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Complications from the sickle cells blocking
blood flow and early breaking apart include

• pain episodes
• strokes
• increased infections
• leg ulcers
• bone damage
• yellow eyes or jaundice
• early gallstones
• lung blockage
• kidney damage dehyration
• blood blockage in the spleen or liver
• eye damage
• low red blood cell counts (anemia)
• delayed growth

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Inheritance of Sickle cell anemia

• Normal hemoglobin allele - (N)
• Sickle cell hemoglobin allele (S)
• Normal RBCs (NN)
• Carrier for Sickle cell anemia (NS)
• Sickle Cell Anemia (SS)

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Where is it found?

• Basically found in people of African decent.
• 19 of Americans of African ancestry.
• 40 of population of Africa carry the trait.
• Carriers of SC anemia (NS) have a partial
  resistance to MALARIA
• Malaria Sickle Cell Anemia

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Problems

• 1. A woman who is a carrier for SCA has children
  with a man who does not have an allele for SCA.
  What could their children be?
• 2. What are the chances of a carrier having a
  child without the SCA allele with a person who
  has SCA?

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Polygenic Inheritance

• Some human traits are controlled by more than one
  set of genes that determine the expression of the
  traits.
• Ie. Eye color, hair color, height, body weight,
  skin color, etc

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Multiple Alleles

• For some traits, there are more than 2 alleles
  for a given trait.
• Ie. Blood types There is the A, B and o alleles
• Karl Landsteiner in 1900 discovered the ABO blood
  typing system in humans

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• With the two blood antigens (proteins located on
  the RBC)
• A B gt o
• A type blood contains the A antigen (blood
  protein) on its RBCs.
• Produces anti-B antibodies
• B type blood has the B antigen on its RBCs.
• Produces anti A antibodies
• AB blood has both A B antigens
• Produces no antibodies against the 2 types of
  blood proteins
• O blood contains no blood antigens
• Produces both anti A anti B antibodies

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• When a person with type A is given type B blood
  in a transfusion, the persons blood starts
  producing anti B antibodies, causing the blood
  cells to agglutinate (clump up).
• This is a type of transplant rejection.

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What mixes with what?

• Blood type Can donate to Can
  receive from
• A A, AB A, O
• B B, AB B, O
• AB AB A, B, AB, O
• O A, B, AB, O O
• Universal donor Universal receiver

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Problems

• Figure out what blood type two parents must be in
  order to have 4 children, each with a different
  blood type.
• 2. Who could be the father? A woman with O
  type blood has a child with B type blood
• Man 1 is A type blood
• Man 2 is AB blood
• 3. What could be your blood type?

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What is with the and with blood types?

• Rh factor Additional blood antigens named
  after the Rhesus monkey
• Rh - has the Rh antigen
• Rh- doesnt have the Rh antigen
• Produces anti Rh antibodies
• Rh is dominant over the Rh- allele.

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• Problem may arise with a woman who is Rh- having
  a child with a man who is Rh.
• Since Rh is dominant, the child she is carrying
  most likely is Rh.
• At birth, there is a mixing of maternal and fetal
  blood (at the placenta). Immediately, the
  mothers blood starts to build up anti Rh
  antibodies.
• Since 1 child is born and away from the mother,
  there is no problem for this child. With each
  additional birth though, the mothers blood has
  antibodies to the childs blood. Fetal blood
  agglutinates, possibly causing still births.
• Problem solved by giving the mother a Rogam shot.
  Actually, this is an anti- anti Rh shot.
  Makes it like she never had a child.