5.5 Genetic Tools - Pedigrees

Determining PATTERN OF INHERITANCE

• DEDUCTION IS BETTER THAN INDUCTION!

  • Always eliminate choices first

  • Find broken rules to eliminate options

• After eliminating all possible options determine which is would be more likely

  • Usually this happens with sex linked conditions

  • You cannot always find a definitive answer

Autosomal Dominant

1. If an offspring has it, at least 1 parent has it

2. It cannot SKIP generations - always a direct line of inheritance

Autosomal Recessive

1. If both parents have it, ALL offspring have it

Sex (X) Linked Dominant

Rules

1. If an offspring has it, at least 1 parent has it

2. It cannot SKIP generations

3. If a father has it, ALL daughters have it

4. If a son has it, his mother has it

FEMALE bias (not a rule)

can never be 100% sure it’s XLD and not Autosomal Dominant

Sex (X) Linked Recessive

1. If both parents have it, ALL offspring have it

2. If a mother has it, ALL sons have it

3. If a daughter has it, her father has it

MALE bias (not a rule)

Sex (Y) Linked

1. If a father has it, ALL son will have it

2. if a father DOESN’T have it, NO sons have it

3. No females have it

Mitochondrial Inheritance

1. If a mother has it, ALL offspring have it

2. if a mother does NOT have it, NO offspring have it

Determing Genotypes (Autosomal)

1. Determine the inheritance (AD)

2. Genotype all homozygous recessives

3. Give all dominant phenotypes 1 A

4. Make sure all parents and offspring of a homozygous recessive have 1 a