Pedigree Charts

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Pedigree Charts

• The family tree of genetics

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Overview

• What is a pedigree?
• Definition
• Uses
• Constructing a pedigree
• Symbols
• Connecting the symbols
• Interpreting a pedigree

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What is a Pedigree?

• A pedigree is a chart of the genetic history of
  family over several generations.
• Scientists or a genetic counselor would find out
  about your family history and make this chart to
  analyze.

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Constructing a Pedigree

• Female

• Male

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Connecting Pedigree Symbols
Examples of connected symbols

• Married Couple
• Siblings

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Connecting Pedigree Symbols
Examples of connected symbols

• Fraternal twins
• Identical twins

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Additional Symbols
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Male-DAD
Female-MOM
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Symbols in a Pedigree Chart

• Affected
• X-linked
• Autosomal carrier
• Deceased

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Interpreting a Pedigree Chart

• Determine if the pedigree chart shows an
  autosomal or X-linked disease.
• If most of the males in the pedigree are affected
  the disorder is X-linked
• If it is a 50/50 ratio between men and women the
  disorder is autosomal.

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Example of Pedigree Charts

• Is it Autosomal or X-linked?

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Answer

• Autosomal

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Interpreting a Pedigree Chart

• Determine whether the disorder is dominant or
  recessive.
• If the disorder is dominant, one of the parents
  must have the disorder.
• If the disorder is recessive, neither parent has
  to have the disorder because they can be
  heterozygous.

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Example of Pedigree Charts

• Dominant or Recessive?

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Answer

• Dominant

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Example of Pedigree Charts

• Dominant or Recessive?

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Answer

• Recessive

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Ff

• Steps
• Identify all people who have the trait.
• For the purpose of this class all traits will be
  given to you. In other instances, you would have
  to determine whether or not the trait is
  autosomal dominant, autosomal recessive, or
  sex-linked.
• In this example, all those who have the trait
  are homozygous recessive.
• Can you correctly identify all genotypes of this
  family?
• F- Normal
• f- cystic fibrosis

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Pp
Pp

• PKU
• P- Unaffected
• p- phenylketonuria

pp
Pp
pp
PP or Pp
pp
Pp
Pp
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• H-huntingtons disease
• h-Unaffected

Hh
hh
Hh
Hh
hh
hh
hh
Hh
hh
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Summary

• Pedigrees are family trees that explain your
  genetic history.
• Pedigrees are used to find out the probability of
  a child having a disorder in a particular family.
• To begin to interpret a pedigree, determine if
  the disease or condition is autosomal or X-linked
  and dominant or recessive.

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Family Pedigree Lab

• The ability to taste certain chemicals is
  controlled by a single gene.
• Sodium Benzoate
• Thiourea
• PTC
• In this lab you will construct three pedigree
  charts for your family.

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What You Need

• Three pedigree forms titled as follows
• Your Name, Pd. on the top left
• Chemical used on top right
• Sodium Benzoate (Pink)
• Thiourea (Yellow)
• PTC (Blue)
• Three strips of each taste paper, including the
  control

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• Fold strips into forms and paperclip them
  together
• Determine how many relatives you can test
• Cut papers into enough pieces so that each
  relative has a fresh paper
• Test by placing paper on tip of tongue
• Record as a Taster or Nontaster (USE PENCIL)

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Mitochondrial Inheritance
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Dominant Inheritance
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Dominant Inheritance
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Autosomal Dominant
Polydactyly HD Achondroplasia Progeria
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Autosomal Recessive

• Disorders
• Cystic Fibrosis
• Tay-sachs Disease

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X-Linked Recessive Trait
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X-Linked Recessive Trait
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                                                                                                                                                                    Autosomal Recessive.  Trait appears only when two parents by chance carry the hidden allele.                                                                                                                                                                     X-linked Recessive.Mother passes on to half  of sonshalf of daughters carry it.  Father never passes on trait.
                                                                                                                                                                    Autosomal Dominant. Trait appears in every generation, in about half of descendants (assuming a heterozygous carrier.)                                                                                                                                                                     X-linked Dominant.  Father passes trait to all daughters no sons.  Mother passes on to half of children.

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Karyotypes

• To analyze chromosomes, cell biologists
  photograph cells in mitosis, when the chromosomes
  are fully condensed and easy to see (usually in
  metaphase).
• A picture of chromosomes arranged in this way is
  known as a karyotype.

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Karyotypes

• The karyotype is a result of a haploid sperm (23
  chromosomes) fertilizing a haploid egg (23
  chromosomes).
• The diploid zygote (fertilized egg) contains the
  full 46 chromosomes. (in humans)

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Normal Human Male Karyotype 46,XY
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Normal Human Female Karyotype 46,XX
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Labeling a Karyotype

• To label a karyotype correctly, first list the
  number of chromosomes found in the karyotype. Ex.
  46
• Secondly, list the type of sex chromosomes found
  in the karyotype. Ex. XX
• Lastly, list the any abnormalities at the
  appropriate chromosome number.

Normal Human Female 46, XX Normal Human Male
46, XY
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What are abnormalities?

• Sometimes, during meiosis, things go wrong.
• The most common error is nondisjunction, which
  means not coming apart.
• If nondisjunction occurs , abnormal numbers of
  chromosomes may find their way into gametes, and
  a disorder of chromosome numbers may result.

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Autosomal Chromosome Disorders

• Two copies of an autosomal chromosome fail to
  separate during meiosis, an individual may be
  born with THREE copies of a chromosome.
• This is known as a Trisomy
• Trisomy 13, Trisomy 18, Trisomy 21.

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Down Syndrome

• Most common, Trisomy 21 (down syndrome)
• 1 in 800 babies born in U.S. with Trisomy 21.
• Mild to severe mental retardation
• Increased susceptibility to many diseases and a
  higher frequency of other birth defects.

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Sex Chromosome Disorders

• Turners Syndrome (nondisjunction)
• Female inherits only one X chromosome
• Karyotype 45, X
• Women are sterile, sex organs do not develop at
  puberty.
• Klinefelters syndrome (nondisjunction)
• Males receive an extra X chromosome
• Karyotype 47, XXY
• The extra X chromosome interferes with meiosis
  and prevents ind. from reproducing.