Except for certain moments - when cells are dividing, for instance - chromosomes don't form compact, countable bodies inside cells. Instead, they unravel and flop about, which makes counting chromosomes a bit like counting strands of ramen in a bowl.

Mutations can arise anywhere in the genome, in gene DNA and noncoding DNA alike. But mutations to genes have bigger consequences: They can disable proteins and kill a creature.

Junk DNA - or, as scientists call it nowadays, noncoding DNA - remains a mystery: No one knows how much of it is essential for life.

Sam Kean Quotes