Dog Vaccination Schedule. Age. Vaccination. 5 weeks. Parvovirus: for puppies at high risk of exposure to parvo, some veterinarians recommend vaccinating at 5 weeks. Check with your veterinarian. 6 & 9 weeks. Combination vaccine * without leptospirosis.*Some puppies may need additional vaccinations against parvovirus after 15 weeks of age. Consult with your local veterinarian. Â§ According to the American Veterinary Medical Association, dogs at low risk of disease exposure may not need to be boostered yearly for most diseases.
In population genetics, directional selection is a mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.
On each graph, the x-axis variable is the type of phenotypic trait and the y-axis variable is the amount of organisms. Group A is the original population and Group B is the population after selection. Graph 1 shows directional selection, in which a single extreme phenotype is favored. Graph 2 depicts stabilizing selection, where the intermediate phenotype is favored over the extreme traits. Graph 3 shows disruptive selection, in which the extreme phenotypes are favored over the intermediate. Stabilizing selection (not the same thing as negative selection) is a type of natural selection in which genetic diversity decreases and the population mean stabilizes on a particular trait value.