Pedigree – a graphic representation of genetic inheritance

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Pedigree
Section 14-1

• Pedigree a graphic representation of genetic
  inheritance
• Circle usually represents a female
• Square usually represents a male
• Shaded circles and squares represent
  individuals showing the trait being studied
• Unshaded do not show the trait
• Half-shaded circles and squares represent a
  carrier.

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Figure 14-3 A Pedigree
Section 14-1
A circle represents a female.
A square represents a male.
A horizontal line connecting a male and female
represents a marriage.
A vertical line and a bracket connect the parents
to their children.
A half-shaded circle or square indicates that a
person is a carrier of the trait.
A circle or square that is not shaded indicates
that a person neither expresses the trait nor is
a carrier of the trait.
A completely shaded circle or square indicates
that a person expresses the trait.
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• Pedigree Activity

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Karyotype

• Karyotype chart of chromosome pairs that may be
  used to determine a genetic disorder.
• Homologous- matching chromosomes
• Autosomes- chromosomes that are not sex
  chromosomes normally humans have 22 pair
• Sex Chromosomes the 23rd pair of chromosomes
  females have a matching set of homologous
  chromosomes (XX), males do not (XY)

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• Karyotype Picture

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Gender Benders
Interest Grabber
Section 14-2

• You may remember that in humans, the sperm cells
  may carry an X chromosome or a Y chromosome,
  while egg cells have only X chromosomes.
  Sometimes, errors during meiosis in one of the
  parents produce offspring with an abnormal number
  of sex chromosomes.

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Nondisjunction
Disorders

• Changes in Chromosome Numbers
• Nondisjunction failure of chromosomes to
  separate properly during the process of meiosis
• Down Syndrome (Trisomy 21) extra 21st
  chromosome
• Turner Syndrome individual is missing a sex
  chromosome 45XO
• Klinefelter Syndrome individual has an extra X
  chromosome 47 XXY

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Disorders

• Codominance in Humans
• Sickle Cell Anemia affects black Americans
  whose families originated in Africa and in white
  Americans whose families originated in the
  countries surrounding the Mediterranean Sea. An
  individual who is homozygous for sickle cell will
  suffer from the disease. If the person is
  heterozygous, they only carry the disease. They
  are codominant for the disease. In sickle cell
  the protein hemoglobin differs by one amino acid.
  This defective hemoglobin forms crystal-like
  structures that change the shape of the red blood
  cells.

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Sickle Cell

• Picture of a sickle cell

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Genetic Disorders

• Tay-Sachs disease -recessive disorder of the
  central nervous system affects individuals of
  Jewish descent.
• Phenylketonuria (PKU)-a recessive disorder that
  results from the absence of an enzyme that
  converts one amino acid to a different amino
  acid.
• Cystic fibrosis -common genetic disorder among
  white Americans. It is due to a defective
  protein in the plasma membrane. CF results in
  the formation and accumulation of thick mucus in
  the lungs and digestive tract.

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Figure 14-8 The Cause of Cystic Fibrosis
Section 14-1
Chromosome 7
CFTR gene
The most common allele that causes cystic
fibrosis is missing 3 DNA bases. As a result,
the amino acid phenylalanine is missing from the
CFTR protein.
Normal CFTR is a chloride ion channel in cell
membranes. Abnormal CFTR cannot be transported
to the cell membrane.
The cells in the persons airways are unable to
transport chloride ions. As a result, the airways
become clogged with a thick mucus.
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• Sex-Linked Traits in Humans
• Red green color blindness cannot
  differentiate between red and green.
• XCY normal
• XcY colorblind
• XCXC normal
• XCXc normal
• XcXc colorblind

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Figure 14-13 Colorblindness
Section 14-2
Father (normal vision)
Normal vision
Colorblind
Male Female
Daughter (normal vision)
Son (normal vision)
Mother (carrier)
Daughter (carrier)
Son (colorblind)
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Sex Linked Traits in Humans

• Hemophilia X-linked disorder that causes a
  problem with blood clotting.
• XHY normal
• XhY hemophilia
• XHXH normal
• XHXh normal
• XhXh hemophilia

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• Multiple Alleles in Humans
• ABO blood groups are determined by multiple
  alleles.
• Type A contains A antigens (alleles)
• Type B contains B antigens
• Type AB contains both A and B
• Type O has neither A nor B
• Table 12.3 page 331
• Rh antigen positive has the antigen
• Negative does not.
• O universal blood donor
• AB universal blood recipient

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Bioethics and You
Interest Grabber
Section 14-3

• As you become more aware of scientific advances
  in genetics, you might realize that with the
  ability to manipulate genes, there comes
  responsibility. This ability provides an
  opportunity to improve the lives of many people.
  But there is also a potential for errors or
  intentional misuse of the technology.

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Interest Grabber continued
Section 14-3

• Working with a partner, answer the following
  questions.
• 1. In what type of situation do you think genetic
  engineeringchanging the genes of organismsis
  warranted? Explain your reasoning about your
  position. If you do not think that genetic
  engineering is ever warranted, explain your
  reasons for your position.
• 2. In what type of situation do you think genetic
  engineering might be misused? Suggest limits that
  might be placed on the manipulation of genes to
  avoid its misuse.

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Video Contents
Videos

• Click a hyperlink to choose a video.
• Human Sex Determination
• Nondisjunction
• Point Mutation

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Video 1
Video 1
Human Sex Determination

• Click the image to play the video segment.

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Video 2
Video 2
Nondisjunction

• Click the image to play the video segment.

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Video 3
Video 3
Point Mutations

• Click the image to play the video segment.

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Internet
Go Online

• Links from the authors on DNA samples
• Career links on geneticists
• More information on the Human Genome Project
• Interactive test
• For links on pedigrees, go to www.SciLinks.org
  and enter the Web Code as follows cbn-4141.

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Section 1 Answers
Interest Grabber Answers

• 1. This pedigree shows the inheritance of
  attached ear lobes. Which parent has attached ear
  lobes?
• The father
• 2. How many children do the parents have? Which
  child has attached ear lobes?
• Three the daughter has attached ear lobes.
• 3. Which child is married? Does this childs
  spouse have attached ear lobes? Do any of this
  childs children have attached ear lobes?
• The second son no yes, the daughter

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Section 2 Answers
Interest Grabber Answers

• 1. On a sheet of paper, construct a Punnett
  square for the following cross XX x XY. Fill in
  the Punnett square. What does the Punnett square
  represent? According to the Punnett square, what
  percentage of the offspring from this genetic
  cross will be males? What percentage will be
  females?
• One half of the offspring will be males the
  other half, females.
• 2. On a sheet of paper, construct a Punnett
  square for the following cross XXX x XY. Fill in
  the Punnett square. How is this Punnett square
  different from the first one you constructed?
  What might have caused this difference?
• One of the gametes has two X chromosomes instead
  of just one. This might have resulted from a
  mistake in meiosis Instead of separating, the
  pair of X chromosomes stayed together.
• 3. How do the offspring in the two Punnett
  squares differ?
• Instead of two XX and two XY offspring, there
  are one XX and one XY (which are normal), plus
  one XXX and one XXY (which are abnormal).

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Section 3 Answers
Interest Grabber Answers

• 1. In what type of situation do you think genetic
  engineeringchanging the genes of organismsis
  warranted? Explain your reasoning about your
  position. If you do not think that genetic
  engineering is ever warranted, explain your
  reasons for your position.
• Students answers likely will include medicinal
  uses of genetic engineering, such as gene therapy
  for genetic diseases and production of needed
  substances such as insulin. Some students may
  object to all genetic manipulations.
• 2. In what type of situation do you think genetic
  engineering might be misused? Suggest limits that
  might be placed on the manipulation of genes to
  avoid its misuse.
• Students answers may include the designing of
  human babies with desirable traits and the
  cloning of humans. Some students may object to
  genetically altered foods.

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