Somatic cell

In contrast, gametes derive from meiosis within the germ cells of the germline and they fuse during sexual reproduction.

[citation needed] The evolution of an immortal germline producing specialized somatic cells involved the emergence of mortality, and can be viewed in its simplest version in volvocine algae.

Weismannist development is relatively rare (e.g., vertebrates, arthropods, Volvox), as many species have the capacity for somatic embryogenesis (e.g., land plants, most algae, and numerous invertebrates).

[citation needed] A large number of species have the chromosomes in their somatic cells arranged in fours ("tetraploid") or even sixes ("hexaploid").

[9] The ovum now no longer needs to be fertilized, because it contains the correct amount of genetic material (a diploid number of chromosomes).

In practice, this technique has so far been problematic, although there have been a few high-profile successes, such as Dolly the Sheep (July 5, 1996 - February 14, 2003)[10] and, more recently, Snuppy (April 24, 2005 - May 2015), the first cloned dog.

[13] Development of biotechnology has allowed for the genetic manipulation of somatic cells, whether for the modelling of chronic disease or for the prevention of malaise conditions.

[14][15] Two current means of gene editing are the use of transcription activator-like effector nucleases (TALENs) or clustered regularly interspaced short palindromic repeats (CRISPR).

[citation needed] Genetic engineering of somatic cells has resulted in some controversies,[16] although the International Summit on Human Gene Editing has released a statement in support of genetic modification of somatic cells, as the modifications thereof are not passed on to offspring.

[17] In mammals a high level of repair and maintenance of cellular DNA appears to be beneficial early in life.