Population DLA 2 Flashcards
What are the assumptions of the Hardy Weinberg?
Population is large
Random mating between individuals
- No consanguineous mating
- No mate selection based on genotype
No new mutations in the population
No migration of individuals into the population
What are the factors causing genetic variations in population/factirs resulting in departure from the hardy Weinberg equilibrium?
- New mutation
- Natural selection
- Genetic drift
- Consanguinity
What is the impact of new mutations?
- Some genetic loci show high mutation rates & there would be a steady increase in the proportion of mutant alleles in the population (hot spots)
- Some mutations show reduced fitness, resulting in loss of the mutant alleles
- A balance of new mutations and reduced fitness stabilizes the mutant gene frequency in the population
Explain the Heterozygote advantage
Sickle cell disease
Sickle cell is inherited in an autosomal recessive pattern. If two parents who are carriers have a child, there is a 1/4 chance of having an affected child and a 1/2 chance of having a carrier
A single amino acid change causes hemoglobin proteins to form fibers when deoxygenated
Under conditions of low oxygen concentration, haemoglobin S molecules aggregate and form fibrous precipitates. This changes the shape of the red blood cells
-Sickle like appearance of red blood cell
Where malaria is endemic, up to 10% of the genes encoding b-globin alleles are of the mutant HbS form
When homozygous this causes sickle cell anemia
In a carrier the malaria parasite is more likely to cause rupture of the red blood cell, reducing the ability of plasmodium to proliferate
This provides an advantage to being heterozygous for the HbS allele
Explain natural selection
- increases the frequency of alleles that promote survival
- Decreases the frequency of alleles that reduce survival
- Sickle cell disease has a high prevalence in Africa
- Persons with sickle cell trait (heterozygotes) are resistant to falciparum malaria
A high frequency of the mutant sickle cell gene in African populations
- B- thalassemia trait is also protective against malaria
- Lots of other blood disorders
What is reproductive fitness?
The prevelance of a genetic disorder in population also depends on the FITNESS of the individual with the disorder
- Fitness depends on survival to reproductive age and fertility of the individual, once reproductive age is reached
- Tay-Sachs disease represents zero fitness due to death to infertility
- Huntington disease has an average fitness, as the disease doesn’t manifest itself until the person carrying the mutation has produced children
- Phenylketonuria, if untreated results in reduced fitness due to intellectual disability and other medical concerns OR if properly treated results in normal fitness
What is genetic drift?
Fluctuations will be encountered, will have very little effect in large populations
-In small populations though, these random events may fix or extinguish
What is th3 founder effect?
Small population- person with recessive allele of gene moves into the population—> new population with higher frequency of the mutant gene
Founder effect coupled with religious, social or geographic isolation would result in a higher frequency of the mutant allele
Higher incidence of albinism in Hopi Indians of Arizona
- Ataxia telangiecstasia, cystic fibrosis common in the Amish from Holmes County, Ohio
- Tay-Sachs disease, Canavan disease, Gaaucher disease are more prevelang in people of Ashkenazi Jewish descent
What is consanguity?
- Mating of individuals who are related to one another
- Related at the second cousin level or closer
- They have common ancestors
- They are more likely to share the same disease causing genes
- Higher incidence of genetic disease in offspring (especially autosomal recessive disease)
What can cause an increased frequency of a mutant allele?
- geographical isolation
- natural selection(heterozygote advantage & improved fitness)
- Consanguity
- High mutation rates of the gene (mutation hot spot)
