4. Mendelian Inheritance II (Exceptions and Complications) Flashcards
Many genetic conditions have population-specific distributions.
Why is it important to study the diversity of genetic diseases in different population groups?
WHY ARE SOME CONDITIONS MORE PREVALENT IN
CERTAIN POPULATION GROUPS?
How does the founder effect produce more genetic conditions?
EXAMPLE OF A FOUNDER POPULATION IN SA:
How does heterozygotic advantage contribute to some conditions being more prevalent in certain population groups?
- Expected that the allele frequency will ______ overtime if it only has a negative result.
- However, areas with _____ outbreaks carriers have a distinct advantage.
decrease
malaria
How does Consanguinity contribute to some conditions being more prevalent in certain population groups?
- Most genetic disorders are caused by ______ mutations,
- Recessive disease mutations are much more common than dominant diseases mutations
- “Dominant” mutations are more easily eliminated by _____ ______.
Humans carry an average of ____ to two disease causing mutations
recessive
natural selection
one
AFRICAN POPULATION: ALBINISM -
Trinucleotide repeat disorders
* Neither ______ dystrophy nor Friedreich’s ataxia has ever been reported in an black patient in South Africa
* Absence of a predisposing chromosomal background (haplotype)
* ________ disease shows some unique features in black individuals.
- Previously thought to be rare in this ethnic group.
- HD in people of African ancestry has been shown to be genetically heterogeneous.
- HD due to mutations in the _____ gene occurs, but on African-specific haplotypes that differ from
those in white patients.
- In addition, a second HD gene (____) has been implicated in African patients with an HD-like
phenotype (HDL2)
- Individuals with HDL2 share many clinical features with individuals with HD - clinically
indistinguishable
myotonic
Huntington
HTT
(JPH3)
CAUCASIANS: CYSTIC FIBROSIS -
Caused by variants in the cystic fibrosis transmembrane
conductance regulator (______) gene
What is the function of the CFTR gene?
In South Africa, approximately
* 1 in ___ individuals in the Caucasian population,
* 1 in ____ in the population of mixed ancestry
* and up to 1 in 90 black Africans carry a CF mutation.
* It is estimated that 1 in 2 000 Caucasian babies, 1 in 12 000 babies of mixed ancestry and up to 1 in 32 000 black African are born with CF in South Africa.
27
55
ASHKENAZI JEWISH POPULATION:
* Several autosomal recessive genetic disorders that are more common in Jewish populations
* Due to population bottlenecks as well as practice of _________ marriages
* Lead to a decrease in _______ diversity
* Higher likelihood that two parents carrying the same mutation will have a child who will then have both mutations
consanguineous
genetic
COMMON CONDITIONS IN THE ASHKENAZI JEWISH POPULATION:
ASHKENAZI JEWISH: TAY-SACHS DISEASE
AFRIKANERS
Several diseases with an unusually high frequency in Afrikaners have been suggested to be the result of founder effects:
AFRIKANER: SCLEROSTEOSIS
INDIAN: THALASSAEMIA
How did INDIAN: THALASSAEMIA originate?
MANAGEMENT AND GENETIC TESTING: (4)
Although in theory _____
dominant inheritance appears to
be the simplest mode of
inheritance, in clinical practice AD
inheritance can be confusing and
unclear
We know a particular disorder is
autosomal dominant
* single gene
* on an autosome
* _______ in one allele is sufficient to cause the
phenotype
But sometimes _______ in the
pedigree is observed
autosomal
mutation
Inconsistency
- It is useful to consider the
possibility of _______
penetrance when considering
apparent inconsistencies in a
family history, such as “skipped
generations“ - If it is possible for some people
to carry a mutation but not
develop the disorder, the
condition is said to have
reduced or _______
penetrance
reduced
incomplete