Patterns of Inheritance

Question 1

Describe the Pedigree tree?

Answer 1

• Square = Male
• Circle = Female
• Shaded = Affected
• Dot = Carrier
• Slashed line = Dead

Question 2

Autosomal Dominant:
Heterozygous or Homozygous?

What is the chance of an affected individuals’ offspring being affected?

Autosomal Recessive:
Heterozygous or Homozygous?

What is the chance of an affected individuals’ offspring being affected?

What will all the offspring of an affected parent be?

Answer 2

• Heterozygous
• 50%
• Homozygous
• 25%
• Carriers

Question 3

X-linked Inheritance:
Between who are the genes never passed?

What is the chance of a CARRIER FEMALE’s offspring being affected?

What will a male with the variant be?

What will all the daughters of an affected father be?

Answer 3

• Father and Son
• 50%
• Affected (can’t be carriers)
• Carriers

Question 4

Mitochondrial Inheritance:
What is it?

Describe mitochondrial DNA

How are the variants passed on?

Mother cell with mutant mitochondria divides by meiosis, what’s the effect?

Answer 4

• Rare disorder through the inheritance of mitochondrial DNA
• Small, circular molecule of DNA (37 genes)
• Passed on maternally; mitochondria of oocyte isn’t incorporated into the zygote = Males have no affected children
• Bottleneck effect; percentage of mutant mitochondria increases over generations

Question 5

What’s the Hardy-Weinberg Principle?

What does the principle assume?

Example: If a disease incidence of Spinal Muscular Atrophy is 1 in 10,000, what is the carrier frequency?

Answer 5

• p + q = 1 AND p² + 2pq + q² = 1
  • p² = Unaffected frequency
  • 2pq = Carriers
  • q² = Affected frequency
• Allele and genotype frequency in a population will remain constant in successive generations, with no other evolutionary influences
• • q² = 1/10000, so q = 1/100
  • As p + q = 1; p = 1 - 1/100 = 99/100
  • Carrier frequency is then: 2pq = 2 x 1/100 x 99/100 = 1/50