Inheritance Patterns Flashcards
How are males represented in a pedigree drawing?
Squares
How are females represented in a pedigree drawing?
Circle
How are siblings represented in a pedigree drawing?
Line above them
How are partners represented in a pedigree drawing?
Line between them
How are affected people represented in a pedigree drawing?
Shaded in
How are carriers represented in a pedigree drawing?
Dots in their shape
How are children represented in a pedigree drawing?
Line down
How are consanguineous partners represented in a pedigree drawing?
Double line
What does SB mean in a pedigree drawing?
Still born
How are people of unknown sex represented in a pedigree drawing?
Diamond
How are miscarriages represented in a pedigree drawing?
Triangle
How is an abortion represented in a pedigree drawing?
Triangle with a line through
How are foetus’ of unknown sex represented in a pedigree drawing?
Diamond with a P inside
How are identical twins represented in a pedigree drawing?
Horizontal line between two diagonal lines
How are non-identical twins represented in a pedigree drawing?
Two diagonal lines
What is penetrance?
The percentage of individuals that carry the mutation and develop symptoms of the disorder
Give some characteristics of autosomal dominant inheritance
- most affected individuals have an affected parent
- both sexes equally likely to inherit the allele
What is the risk for each child of an affected parent in autosomal dominant inheritance?
1/2
Can unaffected siblings of an affected individual pass the mutation on in autosomal dominant inheritance?
No
What are obligate carriers?
Individuals that have the disease causing genotype but haven’t developed the disease
What is variable expressivity?
Variation in the severity or symptoms of disorder between individuals with the same mutation
What is somatic mosaicism?
When a new mutation arises at an early stage in embryogenesis
What does somatic mosaicism mean for the cells of the individual?
The mutation will only be present in some tissues/ cells
What is germ-line/gonadal mosaicism?
When a new mutation arises during oogenesis or spermatogenesis
What does germ-line/gonadal mosaicism mean for the individual?
The mutation is present in a variable proportion of gametes and can be transmitted to the offspring
What does anticipation mean in autosomal dominant inheritance?
Worsening of disease severity in successive generations
When does anticipation characteristically occur?
In triplet repeat disorders
Give some characteristics of autosomal recessive inheritance
- may be due to consanguinity
- usually one generation is affected
- both sexes are affected and its transmissible between sexes
Are heterozygotes affected by autosomal recessive inheritance?
No
What genotypes are affected by autosomal recessive inheritance?
Homozygous and compound heterozygous
What does compound heterozygous mean?
Two different mutations on the same gene which basically causes homozygosity
What is the recurrence risk for a sibling of an affected person in autosomal recessive disease?
1/4
What is the carrier risk for a sibling of an affected person in autosomal recessive disease?
2/3
What does it mean for males and females if an X-linked trait is recessive?
Males can only be hemizygous but females can be homozygous or heterozygous
What does it mean for males and females if an X-linked trait is recessive?
Women are unaffected carriers and there is no male -> male transmission
What does it mean for males and females if an X-linked trait is dominant?
Women are affected and males are more severely affected and could be lethal
What is the likelihood a child of a carrier female will inherit the X-Linked mutant allele?
50%
What is skewed X-Inactivation?
Generally random but roughly 10% of women have it
What is a manifesting carrier of an X-linked condition?
When a women has some symptoms in X-linked recessive conditions even if they’re heterozygous
What is another term for Y linked inheritance?
Holandric
How is holandric inheritance passed on?
Father -> son
What are the two types of insertion and deletion?
Inframe or frameshift
What is an inframe insertion or deletion?
When the indel is divisible by a multiple of 3
What is a frameshift insertion or deletion?
Not a multiple of three
Is an inframe or frameshift indel more likely to be disease causing?
Frameshift
