Pedigree Analysis

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Pedigree Analysis
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Why do pedigree analysis?

• Problems with human genetics
• human generation span 20-30 years
• parents produce fewer offspring
• breeding experiments are unacceptable

• Solution
• analyze results of matings that have already
  occurred
• collect history for a trait and assemble
  information into a family tree ? pedigree
• can help in predicting the traits of future
  offspring

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• Pedigree symbols

• Pedigree of a family afflicted with
  neurofibromatosis,
• an autosomal dominant genetic disorder

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Inheritance patterns in pedigrees

1. autosomal dominant
2. autosomal recessive
3. x-linked dominant
4. x-linked recessive
5. y-linked

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Autosomal dominant inheritance pattern

• Due to a dominant gene on an autosome
• Characteristics
• males and females are equally affected
• every affected individual has at least one
  affected parent
• affected individuals mating with unaffected
  individuals have at least a 50 chance of
  transmitting the trait to each child
• two affected individuals may have unaffected
  children
• phenotype generally appears every generation
• Examples achrondoplasia, Huntingtons disease,
  widows peak, dimples, free lobes,
  tongue-rolling, brachydactyly, hypercholesterolemi
  a

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Autosomal recessive inheritance pattern

• Due to a recessive gene on an autosome
• Characteristics
• males and females are equally affected
• affected individual may have unaffected parents
• all children of two affected individuals are
  affected
• phenotype may skip a generation
• Examples cystic fibrosis, phenylketonuria,
  galactosemia, albinism, hemophilia, sickle-cell
  anemia, Tay-Sachs disease

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x-linked dominant inheritance pattern

• Due to a dominant allele on the x-chromosome
• Characteristics
• trait is never passed from father to son
• all daughters of an affected male and a normal
  female are affected
• all sons of an affected male and a normal female
  are normal
• females are more likely to be affected than males
• Examples hypophosphatemia, Aicardi syndrome,
  fragile X syndrome

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Some X-linked dominant diseases are lethal for
males
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x-linked recessive inheritance pattern

• Due to a recessive allele on the x-chromosome
• Characteristics
• trait is never passed from father to son
• Males more likely to be affected than females.
• trait or disease typically passed from an
  affected grandfather, through carrier daughters,
  to half of his grandsons
• Examples red and green colorblindness,
  hemophilia, Duchenne muscular dystrophy, Hunter
  syndrome

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y-linked inheritance pattern

• Due to an allele on the y-chromosome
• Characteristic when a male is affected, all of
  his male children are affected
• Examples male infertility and hypertrichosis
  pinnae

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Identify the inheritance pattern for the
following pedigrees and write the possible
genotypes of each individual.

• 1.

• 2.

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Identify the inheritance pattern for the
following pedigrees and write the possible
genotypes of each individual.

• 3.

• 4.

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Identify the inheritance pattern for the
following pedigrees and write the possible
genotypes of each individual.