Question

(1) (26 pts) In lecture we talked about how demographic forces and natural selection can affect patterns of polymorphism (i.e. genetic variation within species).

(a) Describe 2 patterns in genetic variation data (e.g. polymorphism data) that can be caused by balancing selection.

(b) List three ways a bottleneck can affect genetic variation.

(c) Describe 2 approaches one can use to distinguish bottlenecks from selection scenarios at generating the pattern in the data.

Answer 1

The patterns of polymorphism are seen due to the demographic forces which act on the organism as like the environmental condition which can many times evolve the organism and many times suppress it and also can be extinct. due to the demographic forces, the organism has found variation in the genome level which can be found in plant-like Arabidopsis thaliana. which have high range of growing most of the places of the earth the nucleotide and molecular studies of A.thaliana show the sample plants collected by various places showing various changing factor in the genome of that particular plant due to the modifying gene by the demographic forces it can survive in the many places of the earth? the natural selection is always act on all the organisms on the planet evolution is the slow process but the key factor of the evolution is the natural selection by this mechanism nature selects the best one by its capacity for existence called survival of fittest. and both factors especially can change the patterns of polymorphism in the plants.

The genetic variation comes in the population by natural selection and natural selection is the process where the natures select the better candidate for the future generation for the selection many criteria are available with respect to the habitat and the fitness of that organism. Genetic variation among natural populations can develop due to a number of factors that include geographical isolation, ecological isolation, and historical processes. geographical isolation like the genetic drift in nature the one metapopulation can be divided it's in two subpopulation by any kind of barrier like any catastrophic activity happens and they isolate from each other some members can grow one side and other to the other sid both have a different environment and due to this, they evolve on the conditions present in their area as and then the consider as a different species. ecological isolation can be the same mechanism but the criteria that can use in this situation the organism of the same species can be isolated by the ecological isolation and ultimately it leads to the new characters in the organisms and finally comes to new species after a long period of time. current patterns of genetic diversity may reflect historic conditions or events, even if these influences are no longer present. spatial genetic patterns reflect the regional dynamics of a species — how plant populations interact on a larger regional or landscape level. Different plant species display different regional dynamics: they differ in the amount and direction of genetic connection (gene flow) among the populations. Sometimes there are larger populations that are relatively stable over time and act as the source of new genes for smaller, less stable populations or as foundation stock for new populations.

A population bottleneck effect or genetic bottleneck effect is a sudden reduction in the size of a population due to environmental events such as catastrophic activity as famines, earthquakes, floods, fires, disease, and droughts or anthropological activity such as genocide and human population planning. due to these events it reduces the variation in the gene pool of a population; thereafter a small gene pool of species, a smaller population, with a smaller genetic diversity, remains to pass on genes to future generations of offspring by the sexual reproduction. Genetic diversity remains lower, and it increases only when gene flow from another population occurs or very slowly increasing with time as random mutations occur. This gives in a reduction in the robustness of the population and in its ability to adapt to and survive selecting environmental changes, such as climate change or a shift in available resources. Alternatively, if survivors of the bottleneck are the individuals with the greatest genetic fitness, the frequency of the fitter genes within the gene pool is increased, while the pool itself is reduced. The genetic drift caused by a population bottleneck can change the proportional random distribution of alleles and even lead to loss of alleles. The chances of inbreeding and genetic homogeneity can increase due to smaller population size, and it's leading to inbreeding depression. Smaller population size can also cause deleterious mutations to accumulate.

The bottleneck is the kind of selection scenario but not actual because it does not depend on the behaviour of the organism but depend on the environmental condition that the organism lives in. the bottleneck no dought it selects the species for characters but bot the exactly by the mechanism of evolution it can select the organism on the basis of kind of luck of that organism.