Pattern of Inheritance I Flashcards Preview

Term I: Genetics > Pattern of Inheritance I > Flashcards

Flashcards in Pattern of Inheritance I Deck (13):
1

The mitochondrial genome is not nuclear. How is this significant?

It’s derived from the oocyte mitochondria and thus exhibits matrilineal inheritance

2

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

3

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

4

Who is the lethal cousin of achondroplasia?

Thanatophoric dysplasia (remember they’re allelic)

5

What type of inheritance pattern is shown in thanatophoric dysplasia?

new mutation autosomal dominant; ALL infants with thanatophoric dysplasia are born
to unaffected parents

6

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

7

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

8

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

9

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

10

What’s the penetrance for achondroplasia at birth?

100%

11

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)

12

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

13

What’s an example of a disorder with age-dependent penetrance?

Huntington Disease