Disregarding intermediates, the basic distinction between asexual and sexual reproduction is the way in which the genetic material is processed.
Typically, prior to an asexual division, a cell duplicates its genetic information content, and then divides. In sexual reproduction, there are special kinds of cells that divide without prior duplication of its genetic material, in a process named meiosis.
the origin of chromosomal sex determination may have been fairly early in eukaryotes (see Evolution of anisogamy).
The ZW sex-determination system is shared by birds, some fish and some crustaceans.
Sexual reproduction in eukaryotes is a process whereby organisms form offspring that combine genetic traits from both parents.
Chromosomes are passed on from one generation to the next in this process.
Frequently, physical differences are associated with the different sexes of an organism; these sexual dimorphisms can reflect the different reproductive pressures the sexes experience.
Many species, particularly animals, have sexual specialization, and their populations are divided into male and female individuals.
Conversely, there are also species in which there is no sexual specialization, and the same individuals both contain masculine and feminine reproductive organs, and they are called hermaphrodites. The reason for the evolution of sex, and the reason(s) it has survived to the present, are still matters of debate.
Some of the many plausible theories include: that sex creates variation among offspring, sex helps in the spread of advantageous traits, that sex helps in the removal of disadvantageous traits, and that sex facilitates repair of germ-line DNA.
Sexual reproduction is a process specific to eukaryotes, organisms whose cells contain a nucleus and mitochondria.