Mendelian Inheritance Review

Question 1

Autosomal Recessive Key Pedigree Features:

Answer 1

• Parents unaffected carriers.
• Both parent affected, all kids affected.
• Males = females.
• Phenotype found in siblings.
• Recurrence risk = 25%.

Question 2

Does autosomal recessive have generation skipping?

Answer 2

Yes.

Question 3

Autosomal Recessive Risks:

Answer 3

• Risk of child of either sex being affected: 25%.
• Risk of child of either sex being carrier: 50%.
• Risk of child of either sex NOT being affected: 75%.

Question 4

Autosomal Recessive General Features:

Answer 4

• Individual must be homozygous for recessive allele.
• Reduce or eliminate gene product.
• Often affects enzymes.
• Risk increased by: carrier frequency; consanguinity; inbreeding; genetic isolates

Question 5

Autosomal Dominant Key Pedigree Features:

Answer 5

• Every affected individual has an affected parent
• Males = females.
• Male to male transmission.
• Recurrence risk = 50%.
• Normal siblings of affected individuals have all normal offspring.

Question 6

Does autosomal dominant have generation skipping?

Answer 6

No.

Question 7

Autosomal Dominant Risks:

Answer 7

• Risk of child of either sex being affected: 50%.
• Risk of child of either sex being carrier: 0%.
• Risk of child of either sex NOT being affected: 50%.

Question 8

Autosomal Dominant General Features:

Answer 8

• Incomplete dominance:
  
  • homozygotes more severely affected than heterozygotes.

Question 9

X-linked Dominant Key Pedigree Features:

Answer 9

• Affected M + Normal F:
  
  • all daughters affected
  • all sons normal
• no male to male transmission
• females > males

Question 10

Does X-linked Dominant have generation skipping?

Answer 10

No.

Question 11

X-linked Dominant General Features:

Answer 11

• Affected males have more severe phenotype (no X-inactivation).

Question 12

X-linked Recessive Key Pedigree Features:

Answer 12

• Males >>> females.
• Carrier females usually unaffected depending on X-inactivation.
• Gene transmitted from affected male to all daughters (obligate carriers).
• Mutant allele may be passed through a series of female carriers.

Question 13

X-linked Recessive Risks Normal Male and Carrier Female:

Answer 13

• 50% risk females will be carriers.
• 50% risk males will be affected.

Question 14

X-linked Recessive Risks Affected Male and Normal Female:

Answer 14

• all daughters obligate carriers
• all sons normal
• no male to male transmission

Question 15

X-linked Recessive General Features:

Answer 15

• Female carrier phenotype dependent on X-inactivation.