I need to get some information to understand how this works.

I have a half-brother that I plan to do a DNA test with soon to determine if we are related. Now, I know the general stuff - father passes down Y-chromosome to father and to son. Where I start to get confusion is in the DNA aspect. Males are made up of X and Y. But what I don't understand is, our DNA is different. Even twin brothers have different DNA. So how is it that they can test the Y-Chromosome in one male(myself) and see if it pairs up with another Y-Chromosome(my half-brother)? Aren't the DNA inside of those chromosomes different?

 

Sorry for the dumb question. Biology confuses me. Lol.

Not if you share the same father. Most of the Y-chromosome does not undergo recombination, except for a very small region at one end. This suppression of recombination ensures that the Y-chromosome remains intact through lineages. Furthermore, since you inherited it only from your father, there is only one "sequence" that you can inherit. The reason why the rest of the genome can vary is that both your parents have two copies of each chromosome derived from two different parents. The exception to this is the Y-chromosome.

You have 46 chromosomes. Unless you're twins, you will be able to find differences in 45 of those chromosomes, but the Y chromosome will always be the same in two males who share a father.