Medical Genetics: Genetic Variation Recap

• How many codons are in the genetic code?

  64 codons
• Why is there redundancy in the genetic code?

  Because 64 codons code for only 20 amino acids
• What is the origin of genetic variation?

  Mutation
• What is the difference between mutation and polymorphism?

  Mutation is a change, polymorphism is variation
• What does a substitution variant involve?

  One nucleotide replaced by another
• How is a substitution variant formatted?

  “prefix”“position_substituted”“reference_nucleotide””>”new_nucleotide”
• What does the example g.123A>G represent?

  A substitution of A with G at position 123
• What does the notation c.93+1G>T indicate?

  Substitution of G by T at c.93+1
• What is the correct description for changes involving two or more consecutive nucleotides?

  Described as deletion-insertion (delins)
• What is a point mutation?

  One incorrect base added during DNA replication
• What can a deletion mutation lead to?

  Can lead to a frameshift
• What is an insertion mutation?

  Extra nucleotides added during DNA replication
• What is a chromosomal inversion?

  One region of a chromosome is flipped
• What happens in a translocation mutation?

  Region from one chromosome attaches to another
• How can mutations be classified?

  Spontaneous or induced, somatic or germ cells
• What is a missense mutation?

  Base-pair substitution results in a different amino acid
• What is a conservative substitution?

  Replaces one amino acid with a similar one
• What is a non-conservative mutation?

  Replaces one amino acid with a chemically different one
• What is a silent mutation?

  Results in the same amino acid
• What does a nonsense mutation result in?

  Results in a stop codon and shorter polypeptide
• What are frameshift mutations?

  Deletions or insertions not divisible by 3
• What is an in-frame deletion or insertion?

  Deletion or insertion of a multiple of three nucleotides
• What are the features of autosomal dominant inheritance in Punnett squares?

  • 100% affected if both parents are affected
  • 75% affected if one parent is affected
  • 50% affected if one parent is a carrier
• What are the features of autosomal recessive inheritance in Punnett squares?

  • 0% affected if both parents are carriers
  • 25% affected if both parents are carriers
  • 50% affected if one parent is affected
• What are the features of X-linked recessive inheritance in Punnett squares?

  • 0% affected if father is affected
  • 25% affected if mother is a carrier
  • 100% affected if mother is affected
• What are the features of X-linked dominant inheritance in Punnett squares?

  • 0% affected if father is unaffected
  • 75% affected if mother is affected
  • 50% affected if father is affected
• What are Y-linked traits?

  • Traits passed from father to son
  • Only males are affected
  • No female carriers