How does studying the DNA of different types of organisms provide evidence that all life on Earth is related?

Homologous structures provide evidence for common ancestry, while analogous structures show that similar selective pressures can produce similar adaptations

Not sure what you mean by this question

There are four nitrogenous bases that make up dna. the two pyramidines are thymine and cytosine. the two purines are adenine and guanine. these bases pair in a very specific way. adenine - thymineguanine - cytosine i remember it like this: a tall, good cat.