Autosomal Dominant And Recessive Inheritance

Front 1

Genotype

Back 1

the genetic composition of an individual

Front 2

Phenotype

Back 2

the observable physical expression of a gene or genes

Front 3

Carrier

Back 3

a person that silently carries a recessive trait

Front 4

Non-penetrance

Back 4

the gene is present but unexpressed

Front 5

Reduced penetrance

Back 5

If some people with the mutation do not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance. Often found in familial cancer syndromes

Front 6

Variable expressivity

Back 6

people can express the same gene to different extents

Front 7

New mutation

Back 7

the less the fitness produced by the new mutation, the more likely it has arrived via a new mutation

Front 8

Characteristics of a pedigree expressing an autosomal dominant inheritance pattern

Back 8

- Exists in every generation
- Your immediate parent has it
- Male to female ratio should be close to 50/50
- Male to male transmission can occur (b/c not x-linked)

Front 9

Characteristics of a pedigree expressing an autosomal recessive inheritance pattern

Back 9

- If it’s present more than once, it’s probably with the sibling (horizontal pattern) not more distant relatives
- Not sex linked so equal distribution among sexes
- Parents of an affected child might be consanguineous because it raises the prob that two people with the same recessive allele would come together.

Front 10

‘two thirds rule’ –

Back 10

unaffected child of 2 carriers has a 2/3 chance of being a carrier themself

Front 11

Consanguinity related to risk calculation in autosomal recessive pedigrees -

Back 11

Average = 3-5%, first degree = 40%, first cousins = 6-10%, second cousins = 5-6%,

Front 12

Recurrence risk calculations for an autosomal recessive condition

Back 12

A x B x C x D =
prob that mom is a carrier x prob she will pass on recessive allele x prob dad is a carrier x prob dad will pass it on