NOTES: 14.1-14.2: HUMAN HEREDITY

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NOTES 14.1-14.2 HUMAN HEREDITY
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Human Genes

• ? The human genome is the complete set of genetic
  information
• -it determines characteristics such as eye color
  and how proteins function within cells

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Recessive and Dominant Alleles

• Some common genetic disorders are autosomal
  recessive
• This means that you need two recessive alleles
  (on any of the 44 chromosomesNOT the sex
  chromosomes) to express the disease
• EX Cystic Fibrosis
• Other genetic disorders are autosomal dominant
• Only one allele is needed for the trait to be
  expressed
• EX Huntingtons Disease

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Autosomal Recessive Disorders

• In order to develop an autosomal recessive trait,
  an individual must have the genotype aa
• To be born with a homozygous recessive genotype,
  both parents must be heterozygotes
  (carriers)or homozygous recessive themselves
  (although with most disorders, that is not the
  case)WHY NOT?

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From gene to molecule

• In both cystic fibrosis and sickle cell anemia, a
  small change in the DNA of a single gene affects
  the structure of a protein, causing a serious
  genetic disorder

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What makes an allele dominant or recessive?

• Gene sequence of DNA that codes for a protein
• Usually
• Dominant alleles code for the correct production
  of that protein
• Recessive alleles code for no / wrong protein
  production
• Heterozygous condition the normal (dominant)
  allele will still cause correct protein
  production

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Cystic Fibrosis

• Caused by a recessive allele on chromosome 7
• It is an autosomal genetic disorder
• Causes digestive and respiratory problems
• Death around 20-30 years of age
• How does it happen?
• Three bases are deleted from the protein, which
  removes one amino acid
• The protein cannot fold properly anymore, and is
  destroyed
• Result airway is clogged with mucus

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CF Example

• Cystic fibrosis heterozygotes (Ff)
• just one copy of the normal (dominant) allele is
  enough to supply the cell with the proper
  proteins to function.
• Because of this, the normal allele is considered
  dominant over the recessive allele
• Therefore, a person who is heterozygous does not
  suffer from Cystic Fibrosis

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Sickle Cell Anemia

• ? One DNA base has been changed
• Amino acid is valine, instead of glutamic acid
• Result abnormal hemoglobin
• The abnormal hemoglobin forms crystal-like
  structures that change the shape of the red blood
  cells

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Sickle Cell Anemia

• The abnormal red blood cells are shaped like a
  sickle or a half-moon
• These RBCs slow blood flow, block small blood
  vessels, and result in tissue damage and pain.

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Sickle Cell Anemia

• Three genotypes possible
• 1) HH all healthy hemoglobin
• 2) Hh ½ healthy hemoglobin ½ abnormal
  hemoglobin
• CODOMINANCE!!
• 3) hh all abnormal hemoglobin

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Sickle Cell Anemia

• Individuals who are Hh do not have serious health
  problems and can lead relatively normal lives,
  but-
• They do show some signs of sickle cell anemia if
  the availability of oxygen is reduced
• (i.e. high altitude
• strenuous exercise)

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Pedigree Chart

• Shows how a trait is transmitted from generation
  to generation
• Each row is a generation
• Circles represent females
• Squares represent males
• Shaded in person expresses that trait
• Half shaded in person is only a carrier
• Clear person does not carry or express that trait

pg. 315
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Tay-Sachs Disease

• Autosomal recessive disorder
• Recessive allele results in the absence of an
  enzyme that normally breaks down lipids in the
  central nervous system
• Without this enzyme, the lipids accumulate in the
  nervous system and the affected individual dies

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Phenylketonuria (PKU)

• Autosomal recessive disorder
• Absence of an enzyme to break down the amino acid
  phenylalanine
• The accumulation of phenylalanine causes damage
  to the nervous system
• By avoiding phenylalanine in
• the diet, affected infants
• can avoid the symptoms
• of the disorder

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Autosomal Recessive Traits Pedigrees

• May skip a generation
• Affected individuals are born to 2 carriers
• Males and females affected equally
• KNOWN carriers will be half-shaded init is not
  always possible to know if an individual is a
  carrier

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What about autosomal dominant human traits?

• A single dominant allele inherited from 1 parent
  is all that is needed for a person to show the
  dominant trait.

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Simple Dominant Traits

• Tongue rolling
• Unattached earlobes
• Hitchhikers thumb
• Hair in the middle section of fingers
• Ability to taste PTC

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Autosomal Dominant Traits Pedigrees

• Typically seen in every generation, affecting
  multiple people
• Affected individuals are born to affected
  parent(s)
• Males and females affected equally
• There are NO carriers!
• (you either have it AA or Aa
• or you dont aa)

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Autosomal Dominant Disorder HUNTINGTONS DISEASE

• Rare, but lethal, dominant allele
• Results in a breakdown of parts of the brain
• Onset between the ages of 30 and 50
• No known treatment or cure
• There is a test available to see if you have it
  may help with the decision to start a family
• Every child of an affected individual has a 50/50
  chance of being affected (and passing it down)

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• Cant trace every human trait through a pedigree
  because some genes are polygenic
• Shape of your eyes
• Shape of your ears
• Height
• Eye color
• Also, phenotype is influenced by your environment
  (ex nutrition exercise)
• Average height is 10 cm more than it was in the
  1800s in the US Europe due to nutritional
  improvements
• Genes that are denied a proper environment in
  which to reach full expression in 1 generation,
  can achieve full potential in a later generation
  (genes are inherited, the environment is not)

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REVIEWHuman Blood Groups
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Blood Groups

• Human blood comes in a variety of genetically
  determined blood groups
• Using the wrong blood during a blood transfusion
  can be fatal
• A number of genes help determine blood type but
  we will focus on two
• ABO blood groups
• Rh blood groups

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Blood Groups Rh factor

• The Rh blood group is determined by a single gene
  with 2 alleles positive and negative
• The positive allele is dominant
• You need two Rh- alleles (Rh-/Rh-) to be Rh
  negative

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Rh Factor

• The Rh factor genetic information is also
  inherited from our parents, but it is inherited
  independently of the ABO blood type alleles.
• There are 2 different alleles for the Rh factor
  known as Rh and Rh-.

Mother Father Child
Rh- Rh Rh
Rh- Rh- Rh-
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The Rh Issue Mom Rh- Baby 1 Rh
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ABO Blood Groups

• This is a case of multiple alleles
• There are 3 alleles for this geneA, B, and O.
• ANDA and B are CODOMINANT!
• O is recessive to A and B
• Alleles A and B produce antigens (which are
  carbohydrates) on the surface of red blood cells
• O produces NO antigens

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ABO Blood Groupsthe wrong blood can be FATAL

• Antigens are recognized by the immune system and
  induce an immune response
• If the wrong blood is transfused, the body will
  respond to these antigens by producing
  antibodies
• Antibodies are named for what they attack
• Antibodies bind to the foreign molecule (the
  antigen) and blood clumping will occur, which
  leads to blood clotting, which leads to death

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ABO Blood Groups

• If you have blood type A, then you have
• The A antigen on the surface or your RBCs
• You have anti-B antibodies
• You can receive type A blood and type O blood
• Remember Your antibodies are named for what they
  attackso if you received type AB or type B blood
  then clumping would occur.

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ABO Blood Groups

• Try this cross
• Cross a person whos genotype is IAIA with a
  person who is IAIB.
• Give the possible genotypes and phenotypes

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• Cross a person whos genotype is IAIA with a
  person who is IAIB.
• Gametes IA, IA and IA, IB
• Cross

IA
IA
IA
IAIA
IAIA
IAIB
IAIB
IB
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• Genotypes ½ IAIA, ½ IAIB
• Phenotypes ½Type A, ½ Type AB

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Let's Play the Blood Typing Game!!!
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Human Genes Chromosomes

• Vocabulary
• Sex-linked gene
• Sex-influenced gene
• Key Concepts
• Why are sex-linked disorders more common in males
  than in females?

Lou Gehrig died at 37 of ALS
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Human Genes Chromosomes

• Chromosomes 21 22 are the smallest human
  autosomes
• Chromosome 22 contains approximately 43 million
  DNA bases (approx. 545 genes)
• Chromosome 21 contains approximately 32 million
  DNA bases (approx. 225 genes)
• 1 of these genes is associated with ALS
  (Amyotrophic Lateral Sclerosis)
• Causes a progressive loss of muscle control due
  to the destruction of nerves in the brain and
  spinal cord

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Remember

• Humans have 46 chromosomes (23 pair)
• 2 of them are sex chromosomes ? they determine
  what sex you are
• XX female
• XY male
• 44 of them are autosomes ? they do not determine
  what sex you are

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Who determines the sex of a child?

• The mother or the father?
• THE FATHER!!!!

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Why does the father determine the sex of the
offspring???

• Mom is XX, she can donate either one X chromosome
  or the other X chromosome
• Dad is XY, he can donate either an X chromosome
  or a Y chromosomes.
• If the offspring receives the fathers X, it is
  female
• If the offspring receives the fathers Y, it is
  male

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The Y chromosome

• If a Y chromosome is present, the person is male
• X chromosomes contain genes necessary for growth
  / development
• No cases of a person born with being 45,0Y
• Probably spontaneously aborted (miscarriage)

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Sex Linked Genes

• Genes carried on the X or Y chromosome are
  sex-linked because they are on the sex
  chromosomes
• Many sex-linked genes are found on the
  X-chromosome

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Sex Linked Genes

• All X-linked traits are expressed in males
• WHY???????
• Males only have 1 copy of the X chromosome, while
  females need 2 copies of the defective gene

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Human Sex-Linked Gene Disorders

• 1. COLORBLINDNESS
• 3 human genes associated with color vision are
  located on the X-chromosome
• In males, a defective version of any one of these
  produces colorblindness
• Females must receive 2 copies of the allele to be
  colorblind

XCXc
XCXC
XCY
XcY
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The Test
http//www.toledo-bend.com/colorblind/Ishihara.htm
l
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More Human Sex-Linked Gene Disorders

• 2. HEMOPHILIA
• 2 important genes on the X-chromosome that code
  for proteins that control blood clotting
• A recessive allele in either of these 2 genes may
  lead to hemophilia
• -bleeders disease
• -injections of normal clotting
• proteins prevent death

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Sex-Linked Traits and Pedigrees

• only (or mostly) males are affected
• affected males are born to carrier females
• typically not seen in all generations

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Queen Victorias Legacy in Royal Families of
Europe
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Sex-Influenced Genes

• A persons phenotype is affected by their sex
  (internal environment is differenthormones!)
• Ex Pattern Baldness
• WOMEN MEN
• BB not bald BB not bald
•  
• Bb not bald Bb bald
• bb bald bb bald

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X-Chromosome Inactivation

• Females have 2 X-chromosomes if 1 is enough for
  males, how does the cell adjust to the extra
  x-chromosome in females?
• One X-chromosome is randomly switched off
• Condenses and is called a Barr body

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X-Chromosome Inactivation an example

• Tortoise-shell cats
• ? XBY brown male
• ? XbY orange male

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X-Chromosome Inactivation an example

• Tortoise-shell cats
• ? XBXB brown female
• ? XbXb orange female
• ? XBXb tortoise-shell female
• -Can a male cat have tortoise-shell fur?

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Tortoise-shell cats! (a.k.a. Torties) XBXb