Sequence homology

Sequence homology is when two sequences of DNA, RNA, or proteins are similar to each other. A sequence is like a list of letters in a certain order. For example, ACTG is a sequence of letters used to represent a piece of a gene. When two sequences are "homologous", they are very similar. Sometimes two different kinds of organisms will have the same or very similar sequences, and this can tell us that they both have the same or almost the same genes!