Pedigree Analysis

• Pedigree analysis


  A systematic study of the inheritance patterns of traits or genetic disorders within families
• Pedigree


  A family tree that illustrates the relationships among family members across multiple generations
• Pedigrees


  • Valuable tools for geneticists and researchers as they provide insights into the inheritance of traits or genetic disorders within a family
• Mendelian traits


  Traits controlled by a single gene, which can be either dominant or recessive
• Dominant traits


  Expressed even if only one copy of the gene is present
• Recessive traits


  Require two copies of the gene to be expressed
• By examining the presence or absence of a particular trait among family members, geneticists can deduce the mode of inheritance and predict the probability of its occurrence in future generations
• Pedigrees use specific symbols to represent individuals and their relationships within a family
• Pedigree symbols


  • Squares for males
  • Circles for females
  • Lines to connect individuals
  • Patterns or shading to indicate the presence of a trait or genetic disorder
• Pedigree analysis


  • Helps geneticists identify patterns such as autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked inheritance, and mitochondrial inheritance
• This information can be crucial in understanding the genetic basis of diseases, determining the risk of inheritance for individuals, and providing genetic counseling to families
• Autosomal dominant inheritance


  An affected individual has a 50% chance of passing the trait or disorder to each of their offspring
• Characteristics of autosomal dominant traits

  • Vertical transmission: affected individuals are usually seen in every generation
  • Affected offspring of affected parents: if one parent is affected, their children have a 50% chance of inheriting the trait or disorder
  • Equal frequency in males and females: the inheritance is not influenced by the sex chromosomes
  • Unaffected individuals do not pass on the trait
• Autosomal dominant disorders


  • Huntington's disease
  • Marfan syndrome
  • Hereditary spherocytosis
• Autosomal recessive inheritance


  An affected individual inherits one copy of the mutant gene from each parent
• Characteristics of autosomal recessive traits

  • Horizontal transmission: affected individuals are often siblings or close relatives
  • Carriers: individuals with one copy of the mutant gene but do not express the trait or disorder
  • Equal frequency in males and females: the inheritance is not influenced by the sex chromosomes
  • Consanguinity: increased likelihood of autosomal recessive traits or disorders appearing within a family
• Autosomal recessive traits/disorders


  • Cystic fibrosis
  • Sickle cell anemia
  • Phenylketonuria (PKU)
  • Tay-Sachs disease
• 1. linked dominant inheritance


  An affected individual has a 50% chance of passing the trait or disorder to each of their offspring, regardless of the offspring's sex
• Characteristics of X-linked dominant traits

  • Vertical transmission: affected individuals often appear in every generation
  • Affected fathers pass the trait to all daughters
  • Affected mothers pass the trait to both sons and daughters
  • Lack of male-to-male transmission
• 1. linked dominant traits/disorders


  • Rett syndrome
  • Fragile X Syndrome
  • Incontinentia pigmenti
• 1. linked recessive inheritance


  An affected individual inherits a single copy of the mutant gene on the X chromosome from their carrier mother
• Characteristics of X-linked recessive traits

  • Male predominance: more commonly observed in males
  • Carrier females: have one normal X chromosome and one mutant X chromosome
  • Absence of male-to-male transmission
  • Skips generations
• 1. linked recessive traits/disorders


  • Hemophilia A and B
  • Duchenne muscular dystrophy (DMD)
  • Color blindness
• 1. linked dominant inheritance


  An affected male passes the trait or disorder to all of his sons
• Characteristics of Y-linked inheritance

  • Vertical transmission from father to son
  • Absence of female inheritance
• 1. linked inheritance traits/disorders


  • Male infertility
  • Swyer syndrome
• Mitochondrial inheritance


  Traits or disorders controlled by mitochondrial genes are passed down from mother to child
• Characteristics of mitochondrial inheritance

  • Maternal inheritance: all children of an affected mother have a chance of inheriting the trait or disorder
  • Absence of male-to-offspring transmission
• Mitochondrial inheritance traits/disorders


  • Mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS)
  • Mitochondrial myopathy
  • Leber hereditary optic neuropathy (LHON)
• Autosomal Dominant Disorders


  • Equal frequency in males and females
  • Unaffected individuals do not pass on the trait
• Autosomal Dominant Disorders


  • Huntington's disease
  • Marfan syndrome
  • Hereditary spherocytosis
• Autosomal dominant traits


  Appear equally in males and females
• Autosomal dominant traits appear equally in males and females because the inheritance is not influenced by the sex chromosomes
• Individuals without the trait or disorder do not pass it on to their offspring, as they do not carry the mutant gene
• Autosomal Recessive Traits/Disorders


  • Cystic fibrosis
  • Sickle cell anemia
  • Phenylketonuria (PKU)
  • Tay-Sachs disease
• Autosomal recessive traits/disorders require two copies of the recessive allele to be expressed
• 1. linked Dominant Traits/Disorders


  • Rett syndrome
  • Fragile X Syndrome
  • Incontinentia pigmenti
• 1. linked dominant disorders are more severe in males as they only have one X chromosome
• 1. linked Recessive Traits/Disorders


  • Hemophilia A and B
  • Duchenne muscular dystrophy (DMD)
  • Color blindness
• 1. linked recessive disorders are more common in males as they only have one X chromosome