Ch' 1213: Human Heredity

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Ch. 12-13 Human Heredity

• Vocabulary
• Karyotype
• Sex chromosome
• Autosome
• Pedigree
• Polygenic
• Carrier

Key Concept How is sex determined? How do small
changes in DNA cause genetic disorders?
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Human Chromosomes

• To examine human chromosomes, biologist
  photograph cells in mitosis when the chromosomes
  are fully condensed
• Cut out the chromosomes from the picture and
  group them together in pairs
• This type of picture is called a
• KARYOTYPE

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Karyotypes

• A karyotype can tell you THREE things
• Sex (male or female)
• Irregular numbers of chromosomes
• Any mutations in the chromosomes
• Basically all the chromosomes in a cell are
  displayed and can be examined for any
  abnormalities

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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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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 born with 44
  autosomes and only 1 Y chromosome
• Probably spontaneously aborted (miscarriage)

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Single Gene traits

• Some traits are determined by one gene with 2
  different versions? alleles

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Single Gene Traits 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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What makes an allele dominant or recessive?

• Genesequence 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 conditionthe normal (dominant)
  allele will still cause correct protein
  production

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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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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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Sickle Cell Anemia

• One DNA base has been changed
• Amino acid is valine, instead of glutamic acid
• ResultAbnormal hemoglobin

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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. 243
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Definitions

• Carrier a person who carries the allele for the
  trait but does not express it
• EX Cystic Fibrosis is an autosomal recessive
  disorder
• Carriers genotype Ff
• For a person to have Cystic Fibrosis
  (genotypeff), he or she must have inherited an
  f from both parents
• Therefore, BOTH parents must be carriers (both Ff)

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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 10cm 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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Review

• If a person is a carrier for a trait, what does
  that mean?
• They have the allele for the trait but do NOT
  express it

• What is the difference between an autosome and a
  sex chromosome?
• Sex chromosome determines the individuals sex
  (2), while autosomes are the rest of the
  chromosomes (44)

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Human 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 Groupsthe easy one first

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

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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 AA with a person
  who is AB.
• Give the possible genotypes and phenotypes

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• Cross a person whos genotype is AA with a person
  who is AB.
• Gametes A, A and A, B
• Cross

A
A
A
AA
AA
AB
B
AB
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• Genotypes ½ AA, ½ AB
• Phenotypes ½Type A, ½ Type AB

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Human Chromosomes

• Vocabulary
• Sex-linked gene
• Sex-influenced gene
• Nondisjunction and chromosome mutation
• Key Concepts
• Why are sex-linked disorders more common in males
  than in females?
• What is nondisjunction, and what problems does it
  cause?

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Human Chromosomes

• Your chromosomes contain about 30,000 genes and
  46 chromosomes
• Once thought to be over 100,000 genes
• Thats about 3 billion base pairs
• Remember genes on the same chromosome are linked
  together
• They tend to be inherited together

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Sex Linked Genes

• What are linked genes?
• They can be separated during meiosis through
  CROSSING OVER
• 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

• The X chromosome has many genes that are
  important for growth and development
• The Y-chromosome only contains a few 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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Sex-Linked Gene Disorders

• 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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Sex-Linked Gene Disorders cont.

• Hemophilia
• 2 important genes on the X-chromosome that code
  for proteins 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-Influenced Genes

• A persons phenotype is affected by their sex
• But the trait is on an autosome
• 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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Chromosomal Disorders

• Most of the time, the mechanisms that separate
  human chromosomes in meiosis work very well, but
  things can go wrong
• The most common error NONDISJUNCTION
• The chromosomes fail to separate
• The result? Abnormal numbers of chromosomes

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Nondisjunction

• Prefixes
• dis absence of / opposite of
• non not
• Root Word
• Junction joining together
• disjunction the act of separating
• nondisjunction the act of not separating

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Examples of Chromosomal Disorders

• Down Syndrome
• Klinefelters Syndrome
• Turners Syndrome
• Triple X Syndrome

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Examples of Nondisjunction resulting in
Chromosomal Disorders

• Down's Syndrome 47 chromosomes with 3 21
  chromosomes.
• Triple-X Syndrome 47 chromosomes caused by 3 X
  chromosomes.
• Klinefelter's Syndrome 47 chromosomes caused by
  2 X chromosomes and 1 Y chromosomes.
• Turner's Syndrome 45 chromosomes with 1 X
  chromosome (caused by the absence of one of the X
  chromosomes or a Y chromosome).

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Chromosomal Mutations

• Chromosomal Mutation
• Deletion
• Duplication
• Inversion
• Translocation

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Chromosomal Mutation (structural change)

• Deletion lose all or part of a chromosome
• ABC-DEF AC-DEF
• Duplication segment of a chromosome is repeated
• ABC-DEF ABBC-DEF

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Chromosomal Mutation (structural change)

• Inversion chromosome segment becomes oriented in
  reverse direction
• ABC-DEF ABE-DCF

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Chromosomal Mutation (structural change)

• Translocation part of 1 chromosome breaks off
  attaches to another non-homologous chromosome
  (segment is usually exchanged)

ABC-DEF ABC-JKL GH-IJKL GH-IDEF
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Chromosomal Mutation (change in number)

• If an organism is born with the incorrect number
  of chromosomes
• Ex 47 human chromosomes instead of 46
• Result of nondisjunction

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14-3 Human Molecular Genetics
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DNA FINGERPRINTING

• DNA fingerprinting is a technique developed to
  analyze sections of DNA that have little or no
  known function.
• these areas vary widely from one individual to
  another.
• This technique can be used to identify
  individuals based on banding patterns in the
  resulting DNA fragments
• uses restriction enzymes
• proteins that cuts DNA at specific sites along
  the nucleotide chain (cuts at specific base
  pairs).
• Is used to determine paternity or match a suspect
  to a crime scene (like on CSI!)

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THE PROCESS

• human DNA is cut with restriction enzymes this
  produces DNA fragments of different lengths
• mix the DNA fragments with a probe that glows in
  UV light (the probe will stick to certain
  segments of DNA)

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• run the DNA fragments through a clear gel

negative end
DNA goes in wells at the top

• DNA has a "-" charge
•  DNA will move to the "" end of the gel

positive end
smaller fragments will travel through the gel
faster
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4. Smaller fragments of DNA will travel through
the gel faster (remember the gel is porous).
negative end
Large DNA fragment
positive end
Small DNA fragment
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• 5. In order to see these fragments, the gel is
  viewed under UV light. The result The DNA
  fragments with the probe attached will glow you
  will see a banding pattern

Because each person's DNA is different, the
restriction enzyme will cut the DNA in different
places for different people and every person will
have a different band pattern.
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DNA_DetectivePC.exe
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Gene Therapy

• Gene therapy is the process of changing the gene
  that causes a genetic disorder.
• Technique of replacing a defective gene with a
  healthy version of the gene
• This way, the body can make the correct protein
  or enzyme it needs which eliminates the cause of
  the disorder.
• 1st attempt to cure a genetic disorder by gene
  transfer 1990
• Then, 1999 French girl apparently cured of an
  inherited immune disorder after cells from her
  bone marrow were removed, modified in the
  laboratory, and then placed back in her body

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• Uses a vector to get the new DNA inside your
  cell ? viruses are often used cause they infect
  cells easily.
• How does it work?.
• 1. The virus DNA is modified so it doesnt cause
  
• disease
• 2. DNA containing good gene is spliced to
  viral
• DNA
• The patient is then infected with this newly
  modified virus particles which should carry the
  good gene into the cells and correct the
  disorder.

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Gene therapy today remains a high
risk,experimental procedure. Ethical Questions
raised as we learn more about the human genome
and gene therapy 1. If we can manipulate genes
to cure disease, does this also give us the right
to engineer our bodies? (determine eye color,
whether you are tall/short, hair color, sex,
blood type...) 2. What will be the consequences
if biologists successfully clone human beings?
Science meets Hollywood Issues like these were
the basis of the movie, GATTACA
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Review

• What is the purpose of gene therapy?
• Gene therapy is a process designed to change
  (replace) the damaged or defective gene with a
  normal, functional gene.

• What is a restriction enzyme?
• A restriction enzyme is a protein that cuts DNA
  at specific sites along the nucleotide chain
  (cuts at specific base pairs).