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.
Stabilizing selection commonly uses negative selection (a.k.a. purifying selection) to select against extreme values of the character. Stabilizing selection is the opposite of disruptive selection. Instead of favoring individuals with extreme phenotypes, it favors the intermediate variants.