What is a mutation?

Which of the following characterizes a point mutation?

Sickle cell anemia is an inherited disorder. It affects the shape of red blood cells, which carry oxygen to all parts of the body. Due to the sickle shape, it becomes more rigid, slowing and blocking the blood flow. The disorder is caused by a single nucleotide difference in the hemoglobin gene, which changes glutamic acid into valine. This type of mutation is an example of _______________.

A green parakeet gave birth to five young birds, four of which were green and one of which was yellow. The researcher determined the amino acid sequence for both enzymes responsible for green and yellow pigment production and found the following result:
GREEN: Ala-Gly-Val-Ala-Pro-Thr-Gly-Leu
YELLOW: Ala-Gly-Val-Ala-Thr-Thr-Gly-Leu
Identify which DNA base pair change resulted in the yellow-coloured parakeet.

Deletion or addition of a single nucleotide is often more serious than losing or adding three nucleotides because it can lead to __________ mutation.