There can be a lot of factors that express sexuality. The origin would be its genes. The genetic make-up of the person what trait has passed on to an individual from his parents. Another factor is the environment. A person's sexuality can be influenced by social groups, home environment and from the media that he/she looks at.
DNA replication is said to be semi-conservative because of this process of replication, where the resulting double helix is composed of both an old strand and a new strand. ... Semiconservative replication would produce two copies that each contained one of the original strands and one new strand.