Pattern of Inheritance I Flashcards
The mitochondrial genome is not nuclear. How is this significant?
It’s derived from the oocyte mitochondria and thus exhibits matrilineal inheritance
What are the characteristics of an autosomal dominant disease?
one mutant allele is sufficient to cause the disease, 50% chance of transmission with
each pregnancy, there’s vertical transmission, male to male transmission, affected males
= affected females
What type of inheritance pattern is shown in achondroplasia?
autosomal dominant single gene disorder; it’s a new mutation dominant disorder—
90% of infants with achondroplasia are born to parents with normal stature; increased
new mutation rate associated with advanced paternal age; has 100% penetrance
Who is the lethal cousin of achondroplasia?
Thanatophoric dysplasia (remember they’re allelic)
What type of inheritance pattern is shown in thanatophoric dysplasia?
new mutation autosomal dominant; ALL infants with thanatophoric dysplasia are born
to unaffected parents
True or false: There’s increased instances of Marfan syndrome and Achondroplasia
with advanced paternal age.
A: True; continuous series of mitotic cell divisions in spermatogonia result in 1in 10
having deleterious mutation
What is fitness?
the probability of transmitting one’s genes to the next generation as compared to the
average probability for the population; fact, fitness for TD = 0
What is “brittle bone disease”? What’s its inheritance pattern? What’s the lethal
form?
Osteogenesis imperfecta – inherited disorder of type I collagen; it’s an autosomal
dominant disease; type II is lethal and therefore the reproductive fitness is zero
What is Huntington’s disease?
Autosomal dominant disorder that shows age-dependent penetrance; people who carry
the gene do not know they are affected when they are having children (mean age of
presentation is 35-45 years – age of onset depends on degree of expansion – people with greatest number of repeats have the earliest onset); penetrance is 100% by age 70; it’s a disorder in which all affected have unstable trinucleotide CAG repeat expansion (polyglutamine disorder); characterized by progressive movement disorder, cognitive
decline and changes in personality
What’s the penetrance for achondroplasia at birth?
100%
Compare/contrast the terms penetrance versus expressivity
Penetrance is whether or not the trait is manifested; expressivity is the degree to which
a trait is manifested (contributing factors to variability in expression include modifier
genes, environment, stochastic factors)
What’s an example of a disorder with variable expressivity?
Neurofibramatosis type I; it’s autosomal dominant but have extremely variable
expressivity; development of patches of brown pigmentation (café-au-lait macules),
benign nodules of the iris, axillary or inguinal freckles
What’s an example of a disorder with age-dependent penetrance?
Huntington Disease
