modes of inheritance

• What is the definition of a dominant allele in Mendelian inheritance?

  An allele that masks the effect of another allele
• What is the law of segregation in Mendelian inheritance?

  Each organism has two alleles for each trait, which separate during meiosis
• What is the law of independent assortment in Mendelian inheritance?

  Unlinked gene pairs segregate independently of each other
• What is the law of dominance in Mendelian inheritance?

  In a heterozygous condition, the dominant allele determines the organism's appearance
• What are the four Mendelian inheritance patterns?

  Autosomal recessive, autosomal dominant, X-linked, and Y-linked
• Who developed the Punnett square?

  Reginald Punnett
• What does a Punnett square represent?

  The probability of a trait being passed from one generation to another

  
• What do big letters (Y) represent in a Punnett square?

  Dominant alleles

  
• What do small letters (y) represent in a Punnett square?

  Recessive alleles

  
• What is required for a person to be affected by an autosomal recessive disorder?

  Two mutated alleles in the gene responsible for the disease
• What is the usual mating pattern for autosomal recessive disorders?

  Aa x Aa
• What proportion of offspring from two heterozygous parents (Aa x Aa) will be unaffected homozygous?

  One fourth
• What proportion of offspring from two heterozygous parents (Aa x Aa) will be phenotypically unaffected heterozygous carriers?

  One half
• What proportion of offspring from two heterozygous parents (Aa x Aa) will be homozygotes affected with the disease?

  One fourth
• What is a common feature of autosomal recessive disorders?

  Skipped generations
• Which of the following is an example of an autosomal recessive disease?

  Sickle-cell anemia
• What is required for a person to be affected by an autosomal dominant disorder?

  One copy of the mutated gene

  
• What proportion of offspring from an affected heterozygous parent (Aa) and an unaffected parent (aa) will express the disease?

  One half
• What is a common feature of autosomal dominant disorders?

  Affected offspring have at least one affected parent

  
• Which of the following is an example of an autosomal dominant disease?

  Huntington's disease
• Why are X-linked recessive disorders more frequent in males?

  Males have only one X chromosome
• What is the inheritance pattern of X-linked recessive disorders?

  Affected males are usually born to unaffected carrier mothers

  
• Which of the following is an example of an X-linked recessive disease?

  Hemophilia A
• What is the inheritance pattern of X-linked dominant disorders?

  All daughters of an affected male show the disease

  
• Which of the following is an example of an X-linked dominant disease?

  Fragile X syndrome
• What is a characteristic feature of Y-linked traits?

  Only appear in males
• What is the inheritance pattern of Y-linked traits?

  All male offspring of an affected male are affected

  
• What are the goals of pedigree analysis?

  • Determine the mode of inheritance
  • Determine the probability of an affected offspring for a given cross
• What are the features of autosomal recessive disorders?

  • Skipped generations
  • Both males and females affected
  • Diseased offspring from normal parents
  • Increased consanguinity between parents

  
• What are the features of autosomal dominant disorders?

  • Males and females equally affected
  • Phenotype appears in every generation
  • Affected offspring have at least one affected parent

  
• What are the features of X-linked recessive disorders?

  • More frequent in males
  • Affected males usually born to unaffected carrier mothers
  • Trait skips a generation
  • Not passed from father to son

  
• What are the features of X-linked dominant disorders?

  • All daughters of an affected male show the disease
  • Half of the progeny of an affected heterozygous female show the disease

  
• What are the features of Y-linked traits?

  • Only appear in males
  • All male offspring of an affected male are affected
• What are some examples of autosomal recessive diseases?

  • Sickle-cell anemia
  • Cystic fibrosis
  • Phenylketonuria
  • Albinism
  • Thalassemia
  • Familial Mediterranean fever
• What are some examples of autosomal dominant diseases?

  • Huntington's disease
  • Familial hypercholesterolemia
  • Achondroplasia

  
• What are some examples of X-linked recessive diseases?

  • Hemophilia A
  • Duchenne muscular dystrophy
  • Color blindness
• What are some examples of X-linked dominant diseases?

  • Fragile X syndrome
• What are the characteristics of Fragile X syndrome?

  • Variable expressivity
  • Reduced penetrance
  • Elongated face and broad forehead
  • Mental problems
  • Increased joint mobility
  • Macroorchidism
  • Prominent lower jaw
  • Large protruding ears