Patterns of Inheritance Flashcards
What is Pleiotrophy?
A mutation that can produce multiple distinct phenotypes that may or may not appear in a particular individual
What is a kindred?
A group of human beings each of which is related, genetically or by marriage to ever other member of the group
What is the proband?
Family member who draws attention to a pedirgree
What is an index case?
the clinically affected family member through whom attention is first drawn to a pedigree of particular interest to human genetics
What is penetrance?
The probability that a gene will have any phenotypic expression at all
What is expressivity?
The severity of expression of the phenotype
What are the characteristics of Autosomal dominant inheritance?
- Multiple generations affected
- Males and females are affected in equal proportion
- Male to male is possible
- Each offspring of an affected parent has a 50% of being affected
Describe Polycystic Kidney disease.
- Autosomal dominant
- Renal cysts, progressive renal failure, extrarenal problems
- Late onset
What are the characteristics of Autosomal recessive inheritance?
- Males and females are equally likely to be affected
- Both parents must be carriers to have an affected child
- Recurrence risk is 25% for each offspring of carrier parents
- Certain diseases are more common to certain ehtnicities
- Inquire about consanguinity
Describe Tay-Sachs disease.
Autosomal recessive
Severe mental and physical deterioration and death by 2 or 3
Higher incidence in Ashkenazi Jews
Describe Phenylketonuria (PKU)
Autosomal recessive
Mental retardation, fair skin, eczema, epilepsy
Preventable if prompt dietary treatment
What is Consanguinity?
A genetic relationship where individuals have at least one common ancestor in the preceding few generations
What is an isonymous marriage?
Marriage between persons with the same surname
Not necessarily indicative of consanguinity
What are the characteristics of X-linked recessive inheritance?
- Incidence much higher in males
- All daughters of affected males will be carriers
- Sons of females have a 50/50 chance
Lyonization may make symptoms milder in X-linked recessive disorders. What are some exceptions to this?
- Turner Syndrome (XO)
- Extreme lyonization
- Patients carrying X:autosome translocations
Describe Hemophilia A.
- X-linked recessive
- Coagulation disorder leading to hemorrhaging
Describe Duchenne muscular dystrophy
- X-linked recessive
- Progressive muscle weakness, pseudohypertrophy of calf muscles
What are the characteristics of X-linked dominant inheritance?
Twice as many affected females as males in large population
Affected heterozygous females should transmit to half of offspring
All daughters of affected males will be affected
Describe Rett syndrome
Rare mental retardation syndrome in females, lethal in males
Ataxia, dementa, seizures
X-linked dominant
Describe Hypophosphatemic rickets (Vit D resistant rickets).
X-linked dominant
Ability of kidney to reabsorb phosphate is reduced leading to hypophosphatemia
What are the characteristics of mitochondrial inheritance?
Maternal origin
All offspring of an affected or carrier female are at risk of becoming affected themselves
All daughters of an affected or carrier female are at risk of transmitting the disease
Describe Lever’s hereditary optic neuropathy (LHON)
Rapid, bilateral loss of central vision do to optic nerve death
Affects males and females
Mitochondrial inheritance
Describe Kearns-Sayre Syndrome
External ophthalmoplegia
Pigmentary degeneration of the retina and cardiomyopathy
Mitochondrial inheritance
What are the characteristics of Y-linked (holandric) inheritance?
Only males are affected
Only father to son transmission
What are is pseudoautosomal inheritance?
Pertains to set of genes carried by both the X and Y chromosome, involved with a disorder known as sex reversal
What are the clues to a translocation in a pedigree?
Recurrent miscarriages
Unexplained infertility
Mental handicap associated with unusual or dysmorphic appearance in more tha one individual related through phenotypically normal parents
Child or stillbirth with multiple malformation
What are the 5 drivers for variation from Hardy-Weinberg equilibrium?
Mutation
Gene flow
Selective mating
Genetic drift
Selection
