Same-sex marriage, also known as gay marriage, is marriage between people of the same sex, either as a secular civil ceremony or in a religious setting. Same-sex unions are recorded in the history of a number of cultures, but marriage or similarly formalized same-sex unions were rare or nonexistent in other cultures.
DNA between siblings are similar if you share the same biological parents. The genetic information you gain comes from both of your parents, and are a result of fertilization of 2 haploid cells fusing to form a zygote that has a diploid number of chromosomes.
Siblings who share only one parent have approximately one quarter of their DNA in common. However, DNA does not always copy perfectly, and small errors are common. Small mutations and recombination errors ensure that even twins won't share exactly the same DNA.