Inheritance Pattens

• Mendelian inheritance


  The classic patterns of inheritance seen in single-gene disorders
• Inheritance patterns


  • Dominant inheritance
  • Recessive inheritance
  • Mitochondrial inheritance
  • Multifactorial inheritance
• Autosomal dominant mode of inheritance


  • Abnormal copy of a gene is located on one of the autosomes (chromosomes 1–22)
  • Males and females have the same chance of being affected
  • If one parent is affected, the risk of having an affected child is 50% in each pregnancy
• 1. linked dominant mode of inheritance


  • Abnormal gene is located on one X chromosome
  • Affected father will transmit disease to 100% of his female offspring and none of his male offspring
  • Affected mother has a 50% chance of transmitting disease to any of her offspring
• Autosomal recessive mode of inheritance


  • There are no normal copies of a gene
  • If both parents are carriers, offspring will have a 25% chance of being affected
  • Often seen in only one generation in a pedigree
  • Parental consanguinity increases the risk
• 1. linked–recessive mode of inheritance


  • There are no normal copies of the gene
  • Disease occurs when a son inherits the abnormal copy from his mother
  • No male-to-male transmission
  • Daughters who inherit one abnormal copy are usually asymptomatic, but some may be affected if there is skewed X-inactivation
  • Female who inherits two abnormal copies will always be affected
  • Carrier mother has a 50% chance of having an affected son
• Mitochondrial inheritance


  • Mutation occurs in one of the genes in the mitochondrial genome
  • Mitochondrial genome is only inherited from the mother
  • Offspring of an affected mother can show signs of disease, but an affected father will never have affected offspring
• Multifactorial inheritance


  • Combination of genetic and environmental factors determines whether or not a disorder will manifest
  • Disorder will be seen in a particular family with increased frequency compared with that of the general population
  • Examples include cleft lip and palate, neural tube defects, developmental dysplasia of the hip, and pyloric stenosis