0430 - Population Genetics - EG Flashcards
Roughly how many DNA bases are found in the human genome? How many single nucleotide polymorphisms (SNP) between each pain of haploid DNA sequences?
~3 billion DNA bases and 3 million SNP differences between each pair of haploid DNA sequences.
Define population genetics.
The study of how a population changes over time leading to a species evolving/mutating and the frequency and interaction of alleles and genes in a population.
What is the aim of medical genetics?
To use the principles of population genetics to identify genetic susceptibilities to common diseases and potential treatments. Identifying a burden of genetic disorders within a specific population highlights the need to consider ancestry in assessing an individuals risk of disease.
List the 5 factors influencing the allele frequency within a population.
(1) natural selection. (2) sexual selection. (3) mutations. (4) genetic drift - change in allele frequency due to chance. (5) gene flow - change in allele frequency due to mixing new populations.
What is the Hardy-Weinberg equilibrium?
p + q = 1 . A formulation that states a simple relationship between frequency of alleles at a genetic locus and the genotypes resulting from those alleles. p = dominant allele, q = recessive. p2 + 2pq + q2 = 1
Use a less likely to smoke if you a able to taste the bitter taste of?
phenylthiocarbamide (PTC). autosomal dominant trait.
What index is a measure of how populations differ genetically? How is its result interpreted?
Fst (fixation index)Value of Fst can theoretically range from 0.0 (no genetic difference) to 1.0 (complete genetic difference).Fst = (Ht - Hs)/Ht where Ht is heterozygotes in the total population and Hs is the heterozygotes in the subpopulation.
What are the assumptions (limitations) of the Hardy-Weinberg Equilibrium?
(1) the population is large and mattings are random with respect to the locus in question. (2) individuals of all genotypes must be able to reproduce. (3) no random mutations. (4) must follow Mandelian inheritance (5) no significant immigration of individuals with different alleles to the endogenous population.
Duchenne’s muscular dystrophy (DMD) is a mutation in the structural component of muscle cells which results in a lethal mutation that affects 0.03% of males (x-linked recessive). Why does this lethal mutation not decrease in frequency over time?
DMD is an example of negative selection as those with the mutation do not reproduce. Spontaneous mutations of the dystrophin gene in DMD enable the replacement of those of persons lost from the lethal phenotype, thereby enabling the disease to remain in the population. Roughly 1/3 of those with DMD is due to a spontaneous mutation.
Why does sickle cell anaemia persist in populations?
Due to selective advantage. the autosomal recessive (ss) disease causes hypoxia, yet it also enables resistance to anaemia, for both homozygotes (ss) for the mutation in the Beta globin gene and those heterozygote (Ss - though heterozygotes may not present with hypoxia as will have some normal haemoglobin). Particular selective advantage for Ss who have greatest reproductive fitness.
What is the founder effect? Give an example.
The founder effect is when a disease or catastrophic event reduces the number of people within a population, and a previously rare genotype is then representing a higher proportion and able to develop into higher frequencies with subsequent offspring. For example a catastrophic typhoon in 1775 in Pingelap in Micronesia caused all but 20 people to die, one of which was a carrier for achromatopsia (colour blindness) now this population has 10% of people achromatic, to the rest of the world 1:33000.
