explain why calix’s cells having more dna than a normal cat meant point mutation was not the cause.

Calix’s cells having more DNA than a normal cat ruled out a point mutation because a point mutation only alters the sequence of existing DNA rather than increasing the total amount of genetic material.

In the ExploreLearning Meowsis STEM Case, Calix is a rare male calico cat whose cells contain significantly more DNA mass than normal. The evidence points away from a point mutation for two main reasons:

• No change in total DNA quantity. A point mutation changes, adds, or deletes just a single nucleotide base pair. Swapping one letter in the genetic code does not measurably increase the overall weight or volume of DNA in a cell.
• Evidence of a large-scale chromosomal change. Having measurably more DNA indicates a much larger addition of genetic material. In Calix’s case, this extra mass comes from having an entire extra X chromosome (an XXY genotype) caused by nondisjunction during meiosis.