Sexual reproduction is a form of reproduction which involves the fusion of male and female reproductive cells (gametes) to create a zygote in a process called fertilization. The gametes may come from different individuals or the same individual (self-fertilization), and are created by meiosis, a specialized type of cell division. Gametes have half the number of chromosomes found in other cells from the same organism. During fertilization the chromosomes from the gametes are combined, restoring the usual number of chromosomes in the zygote. Thus, the zygote includes genetic material from both gametes.

Sexual reproduction is the primary method of reproduction for the vast majority of macroscopic organisms, including almost all eukaryotes (which includes animals and plants).[1] Prokaryotes reproduce through asexual reproduction but may display processes similar to sexual reproduction (mechanisms for lateral gene transfer such as bacterial conjugation, transformation and transduction), but they do not lead to reproduction. In Multicellular organism|multicellular eukaryote organisms, an individual is created anew; in prokaryotes, the initial cell has additional or transformed genetic material. In a process called genetic recombination, genetic material (DNA) originating from two different individuals join up so that homologous sequences are aligned with each other, and this is followed by exchange of genetic information. After the new recombinant chromosome is formed, it is passed on to progeny.

The evolution of sexual reproduction is a major puzzle because asexual reproduction should be able to outcompete it as every young organism created can bear its own young. This implies that an asexual population has an intrinsic capacity to grow more rapidly with each generation.[2] This 50% cost is a fitness disadvantage of sexual reproduction.[3] The two-fold cost of sex includes this cost and the fact that any organism can only pass on 50% of its own genes to its offspring. One definite advantage of sexual reproduction is that it prevents the accumulation of genetic defects.[4]


  2. John Maynard Smith The Evolution of Sex 1978.
  3. Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314.
  4. Recombination affects accumulation of damaging and disease-associated mutations in human populations