2. Principles Of Population Genetics Flashcards
Discuss genetic variation in populations (objective)
Answer later
Calculate allele and genotype frequencies (objective)
Answer later
List the assumptions required for the Hardy-Weinberg Law (objective)
Answer later
Discuss each of the exceptions to the Hardy-Weinberg Law (objectives)
Answer later
Assortative Mating
Consanguinity and Inbreeding
Genetic Drift and the Founder effect
Heterozygote advantage and selection
Highlight the important genetic issues in selected populations (objective)
Answer later
Cystic Fibrosis Sickle Cell Disease Tay-Sachs Disease Maple Syrup Urine Disease Navajo Neurohepatopathy
Populations
Large groups of individuals
-typically concerned with the gene and genotype frequencies, the factors that keep them constant and the factors that tend to change them in populations
What is the frequency of p or q allele?
What is the frequency of p2, 2pq, q2?
Hardy-Weinberg Principle (overview)
Way of predicting genotype frequencies from allele frequencies
Assumptions: Large Population Random Mating No effect of recurrent mutation No selection against any phenotype No migration in or out of the population Autosomal locus
Under assumptions, gene and genotype frequency do not change from generations
Hardy-Weinberg Principle (equations)
Assume two alleles: p and q
p+q=1
p2 + 2pq + q2 = 1
p2, q2 are homozygote genotype frequencies
2pq is heterozygote genotype frequency
*USE for Autosomal Recessive Disorders
Hardy-Weinberg Law (two carriers have children)
(2pq)x(2pq)x(1/4)
1/4 is chance of having a recessive genotype child
Medically Important Exceptions to Hardy-Weinberg (list)
Nonrandom mating
- stratification (racial, ethnic, religion)
- assortative (i.e. Deaf marry deaf)
- consanguinity (relatives in common)
- does not change allele frequency, greater risk of having homozygous (i.e. Middle East)
Small populations
- Inbreeding
- Genetic Drift
- Founder Effect
Inbreeding
Differs from consanguinity (know that relatives related, subset of inbreeding)
Mating within a small geographic region, etc
Genetic Drift
In small population, allele frequencies may change just by chance
(Chance which alleles get passed on, some individuals will die or do not reproduce)
Founder Effect
If a mutation is present or arises in single individual, the frequency of the allele may increase in subsequent generations
Cystic Fibrosis (genetic issues)
Caucasians (1:2500 births)
Defect in chloride channel function, thick mucous
Heterozygous advantage against diarrheal diseases such as cholera and typhoid
Sickle Cell Anemia (genetic issues)
Africans from the equatorial region
Corresponds to high rate of malaria
Two HbS have anemia- “sickled” rbc’s. Cells obstruct capillary blood flow leading to intermittent painful crises
Heterozygotes are asymptomatic unless oxygen levels low (high mountains, airplanes), resistant to malaria protozoan
Hetero’s are selected for in malaria areas
Incidence for homozygotes in African Americans is 1:625, carrier is 1:13
Single point mutation in B-hemoglobin that changes a glutamic acid to valine (propensity for hemoglobin to polymerize under low oxygen tension)
Tay-Sachs Disease (genetic issues)
Severe neurodegenerative disorder due to defective activity of hexoaminidase A (enzyme degrades GM2 gangliosides which are lipids in neurons
Ashkenazic Jews
Fatal, no treatment
Small, isolated communities with breeding restricted to those of the same faith/ethnicity
Maple Syrup Urine Disease (genetic issues)
Neurotoxic symptoms in first weeks of life
Inborn error of leucine, isoleucine and valine metabolism (one enzyme affecting 3 aa’s)
High incidence in Mennonites of Eastern U.S. (PA OH IN)
Likely due to genetic drift/founder effect in small population (marriage restricted to same faith)
Navajo Neurohepatopathy (genetic issues)
Degenerative neurologic disease with hepatic and/or neurologic dysfunction
Mutation in MPV17 gene (mitochondrial function)
Population reductions in Navajo because of US military
Frequency of MPV17 mutation likely increased due to genetic drift/founder effect
