Pedigree Charts

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Pedigree Charts

• The family tree of genetics

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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/
• couple with children
• Siblings

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Example

• What does a pedigree chart look like?

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Example of Pedigree Charts

• The Shaded shapes means that person has that
  trait
• They can be homozygous for the trait and if the
  trait is a dominant trait they can be
  heterozygous for the trait

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Patterns of Inheritance

• When analyzing pedigrees, biologists find certain
  phenotypes are repeated in predictable patterns
  from one generation to the next generation
• These patterns are called
  Patterns of Inheritance

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Interpreting a Pedigree Chart

• Determine whether the trait is dominant or
  recessive. (Remember the dominant traits shows
  if there is 1 or 2 alleles RR or Rr, the
  recessive shows only if there are 2 recessive
  alleles - rr )
• If the trait is dominant, one of the parents must
  have the trait.
• If the trait is recessive, neither parent has to
  have the trait because they can both be
  heterozygous.

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Heterozygous vs. Homozygous

• Remember that an offspring gets one allele for a
  trait from each parent thats 2 alleles
• If the alleles are the same, we say that
  offspring is homozygous the same
• If the alleles are different, we say the
  offspring is heterozygous different

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Hetero Homo zygous display

• An example If the offspring has the dominant
  trait for tallness (T) from one parent and the
  recessive trait (t) from the other, then their
  genotype is Tt and they are heterozygous. (They
  are still tall)
• Some pedigrees split their circles
  squares into two and shade them
  according to whether the individual
  is heterozygous or homozygous.

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Example of Pedigree Charts

• Dominant or Recessive?

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Example of Pedigree Charts

• Dominant

Widows peak, Hitchhiker thumb, Cataracts,
Polydactyly, Achondroplasia and Huntingtons
disease are all Dominant traits
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Example of Pedigree Charts

• Dominant or Recessive?

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Example of Pedigree Charts

• Recessive

Cystic fibrosis, Tay-Sachs disease, Sickle Cell
Anemia, and Phenylketonuria are all recessive
traits
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Pedigree vs Punnett Square

• Pedigree
• Follow traits for generations

• Punnett Square
• Predicts the probability of inheriting a trait in
  one mating

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Genetic Disorders

• Diseases or debilitating conditions that have a
  genetic basis
• These disorders can be caused by
• Single allele inheritance
• Multiple allele inheritance
• Polygenic inheritance
• X-linked inheritance
• Sex-Influenced traits
• Nondisjunction

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Traits Controlled by a Single Allele

• There are more than 200 human traits that are
  determined by only ONE allele
• Can be recessive or dominant
• Huntingtons disease is caused b a dominant
  allele on an autosome
• Emerges in a persons 30s, mild forgetfulness,
  irritability, loss of muscle control,
  uncontrollable physical spasms, severe mental
  illness, and eventually death
• 1/10,000 people are affected
• Genetic marker (short DNA segment associated with
  the trait) has been identified
• Cyctic fibrosis (1/2080 whites), albinism,
  Tay-Sachs (1/1600 European descent Jews)
  phenylketonuria (1/18,000), and sickle cell
  anemia (1/500 Africans) are single allele
  recessive traits

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Traits Controlled by Multiple Alleles

• Controlled by three or more alleles of the same
  gene that code for a single trait
• ABO blood types in humans
• Each person has 2 of the 3 alleles IA, IB and I
• IA and IB are codominant (both are expressed)
  when expressed together

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Polygenic Traits

• Most human traits are controlled by several genes
• Polygenic traits are controlled by two or more
  genes
• Skin color is influenced by 3 6 genes each
  responsible for an amount of pigment called
  melanin
• Eyecolor, footsize, and nose length are also
  polygenic
• Human height is polygenic but also influenced by
  the environment (nutrition and disease)

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X-Linked Traits

• Genes only found on the X chromosome
• X-Linked recessive disorders
• Colorblindness (8 of males)
• Hemophilia impairs blood clotting almost
  exclusive in males
• Duchenne muscular dystrophy weakens and slowly
  destroys muscle tissue

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Sex-Influenced Traits

• Presence of male or female sex hormones
  influences the expression of certain human traits
• Pattern baldness is controlled by the B allele,
  which is dominant in males BUT recessive in
  females
• Men and women with BB genotype will lose their
  hair
• Heterozygous BB men will lose their hair but
  women will not
• This occurs because of the higher levels of
  testosterone in men that interacts with BB
  genotype
• Most sex influenced trait alleles are on
  autosomes and will be expressed by only one sex

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Disorders Due to Nondisjunction

• Cause organisms to have an extra or a missing
  chromosome because chromosomes do not separate
  correctly in replication
• In humans non-disjunction produces 45 or 47
  chromosomes
• Monosomy missing 1 chromosome (45/46 in humans)
• Trisomy has 1 extra chromosome (47/46 in humans)
• This is often lethal with a few exceptions
• Down Syndrome Trisomy 21 weak muscles, heart
  defects, short stature, facial characteristics,
  developmentally delayed
• Klinefelters males with XXY males with
  feminine characteristics, infertile and sometimes
  mental retardation
• Turners syndrome females with X females that
  do not sexually mature, infertile

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Summary

• Pedigrees are family trees that explain genetic
  history.
• Pedigrees are used to determine the probability
  of a child having a certain trait in a particular
  family

• .