Asexual reproduction only needs one parent. All the offspring are genetically identical to each other, and their parent. They are clones.
Sexual reproduction needs two parents. Each parent produces sex cells, called gametes:
Each gamete contains half the number of chromosomes that a body cell has. At fertilisation, a male and female gamete fuse or join together. The new cell contains the full number of chromosomes.
Half of its genes have come from the father, and half have come from the mother. The genetic material from both parents has combined to form a unique individual.
Genetic material is randomly mixed during fertilisation. Any two gametes can randomly meet and fuse, producing a unique combination of genetic information in the offspring.