POPULATION SPECIFIC CONDITIONS Flashcards
Many genetic conditions have population-specific distributions
true
- Research opportunities
* Major relevance when offering diagnostic testing.
- Frequencies of the disease may differ between groups, and the mutational basis may be different.
- Inappropriate testing may be performed and important diagnoses may be missed.
- Different mutation-specific therapies may also be required in the future.
WHY ARE SOME CONDITIONS MORE PREVALENT IN
CERTAIN POPULATION GROUPS?
- founder effect
-The loss of genetic variation that occurs when
a new population is established by a very small
the number of individuals from a larger population.
-• New population may be
distinctively different
• Genotypically
• Phenotypically
founder effect
- New population often the very small population
- ↑ inbreeding
- ↓ genetic variation
• Rare alleles will move to one of two extremes
1. Allele is soon lost altogether
2. Allele survives and becomes more dispersed throughout the population
• ↑ frequency of recessive alleles
• ↑ number in individuals homozygous for recessive traits
EXAMPLE OF A FOUNDER POPULATION IN SA
• The Afrikaner population of SA has many features of a founder population.
• Genetic mutation frequencies in the new population
may differ significantly from those in the original
population
true
WHY ARE SOME CONDITIONS MORE PREVALENT IN
CERTAIN POPULATION GROUPS? 2
- heterozygotic advantage
-The heterozygous genotype has a higher relative
fitness than either the homozygous dominant or
homozygous recessive genotype
example= sickle cell anemia
sickle cell anemia
- Affects hemoglobin
- Causes RBC to become sickle-shaped
Signs and symptoms • Anaemia • Shortness of breath • Fatigue • Delayed growth and development • Jaundice • Painful episodes • Organ damage
Autosomal recessive inheritance
heterozygotic advantage
- Carriers (sickle cell trait) are
resistant to malaria - • Expected that the allele frequency will decrease over time if it only has a negative result.
• However, areas with malaria outbreaks carriers have a distinct advantage
3.10-20% of people in certain
parts of Africa are carriers of
SCA
- Strong heterozygotic
advantage
WHY ARE SOME CONDITIONS MORE PREVALENT IN
CERTAIN POPULATION GROUPS? 3
- Consanguinity
-Marriage or reproductive relationship
between two closely related individuals
consanguinity
• Prevalent in many Middle Eastern and Arab
cultures and societies
• Offspring may be at ↑ risk for genetic disorders
because of the expression of AR gene mutations
• CLOSER the relationship the ↑ probability
that offspring will inherit identical copies of faulty
recessive genes
• Most genetic disorders are caused by recessive mutations,
• Recessive disease mutations are much more common than dominant diseases
mutations
• “Dominant” mutations are more easily eliminated by natural selection.
Humans carry an average of one to two disease-causing mutations
true
AFRICAN POPULATION: ALBINISM
• Common among black African populations in Southern Africa
• The average carrier rate for albinism in South Africa is 1 in 30, resulting in 1 in
4000 black South Africans being born with albinism.
Genes associated is involved in producing pigment (melanin)
clinical manifestation of albinism
Clinical manifestation
Fair skin and light-colored hair
Sun exposure increases the risk of skin damage and skin cancer
Reduced pigmentation of the iris and the retina
• Visual problems
• Nystagmus
• Photophobia
CAUCASIANS: CYSTIC FIBROSIS
CF the most common life-limiting disease among people of Northern European
heritage.
- One of the most common autosomal recessive disorders.
- Occurs in all of SA’s diverse population groups
- CF is a multifaceted condition with
- wide clinical variability,
- hundreds of causative CFTR variants,
