Heartworms are spread to dogs through mosquito bites. Up to 14 inches long, a heartworm lives in the heart and the arteries that carry blood from the heart to the lungs. Heartworms affect how the heart functions and how blood clots and is likely to cause death if untreated. Monthly heartworm preventives are effective.
missense mutation. A substitution of a single DNA nucleotide for another. This results in the transcription of a different amino acid than is normally found in the protein coded by the gene. Missense mutations are found in diseases such as sickle cell anemia.
Mutations are defined as random changes in cellular DNA. They change the genetic code for amino acid sequence in proteins, thus introducing biochemical errors of varying degrees of severity. Mutations have been classified as deletions (loss of DNA bases), insertions (gain of DNA bases), and missense or nonsense (substitution of a DNA base). If the mutations affect germ cells (female ova and male spermatozoa), they will be passed to all the cells of the offspring, and affect future generations. Such mutations are called âgermline mutations,â and are the cause of inherited diseases.