Inheritance Patterns & Factors That Complicate Them Flashcards
1
Q
Autosomal recessive
A
- parents of affected individuals are both unaffected carriers
- affected individuals usually seen in a sibship (horizontal clustering)
- males and females equally likely to be affected
- either parent passes on trait to sons and daughters
- expected recurrence risk: 25%
- chance for child of carriers to be a carrier: 2/3
2
Q
Autosomal dominant
A
- affected offspring usually have one affected parent and one unaffected parent
- vertical transmission
- equal number of males and females affected
- either parent passes on trait to sons and daughters
- expected recurrence risk: 50%
3
Q
X-linked recessive
A
- preponderance of disease in males
- none of affected males have affected offspring but all daughters are carriers and half of these women’s sons will inherit the disease
- all males in a kindred are related through one or more carrier females
- none of sons of affected male have the disease (no male-to-male transmission)
- vertical transmission with disease appearing to skip generations
- heterozygous females are usually unaffected but may have variable signs d/t X-inactivation
- expected recurrence risk depends on mating type
4
Q
X-linked dominant
A
- affected males with normal mates have no affected sons but all daughters will be affected (no male-to-male transmission)
- both male and female children have 50% risk of inheriting phenotype from affected female
- twice as many affected females as males may be seen
- vertical transmission
- expected recurrence risk depends on mating type
5
Q
Y-linked
A
- holandric; Y chromosomes contain few genes
- vertical transmission, strictly father to 100% of sons
- 100% males affected, no females affected
6
Q
Mitochondrial
A
- inherited exclusively through maternal line
- all children of affected mother are affected if penetrance complete
- variable penetrance and variable expressivity in families due to heteroplasmy
7
Q
Imprinting
A
phenotype depends on which parent passed on the gene
8
Q
Multifactorial
A
- trait or disorder caused by combination of genetic and environmental factors
- condition may be polygenic
- no characteristic pattern of inheritance
- empiric risk based on direct observation of data
- recurrence risk higher if: closer relationship of relative, more than one family member affected, more severe phenotype in proband, if phenotype more common in one sex and opposite sex affected in family
9
Q
Reduced penetrance
A
- individual with disease-associated genotype may not have disease phenotype
- offspring at risk
10
Q
Age-dependent penetrance
A
- delay of onset of symptoms
- individuals may have children before they know they’re affected
- carriers of disease-causing gene may pass away before onset
11
Q
Variable expressivity
A
- severity of phenotype varies, even within same family
- individual’s presentation may be mild and they’re unaware they’re affected
- expression influenced by environmental exposures and modifier genes
12
Q
Anticipation
A
- more severe expression/earlier age of onset in more recent generations
- sometimes caused by repeat expansions in DNA
- expansion may be more likely to occur when inherited through mother or father depending on condition
13
Q
New mutation
A
- affected proband with no family history of disease (especially AD conditions)
- if genes in other germ cells do not have mutation, risk to siblings not increased over general population and risk to offspring depends on inheritance pattern of condition
14
Q
Germline mosaicism
A
- relatively rare phenomenon
- 2+ offspring affected with no family history (especially AD conditions)
- more than one genetically distinct germ cell line
- increased risk to siblings of affected proband
15
Q
Sex-limited/Sex-influenced
A
phenotype may occur, be much more likely to occur, or may be more severe, in males or females
