The genetic diversity of sexual reproduction, observed in most eukaryotes, is thought to give species better chances of survival. Sexual reproduction was an early evolutionary innovation after the appearance of eukaryotic cells. During sexual reproduction, the genetic material of two individuals is combined to produce genetically-diverse offspring that differ from their parents. The fact that most eukaryotes reproduce sexually is evidence of its evolutionary success. In many animals, it is actually the only mode of reproduction.
Sexual Reproduction and the Evolution of Sex
BBC - Earth - The real reasons why we have sex
Sexual reproduction, an important source of genetic variability, allows the fungus to adapt to new environments. The process of sexual reproduction among the fungi is in many ways unique. Whereas nuclear division in other eukaryotes , such as animals, plants, and protists, involves the dissolution and re-formation of the nuclear membrane, in fungi the nuclear membrane remains intact throughout the process, although gaps in its integrity are found in some species. The nucleus of the fungus becomes pinched at its midpoint, and the diploid chromosomes are pulled apart by spindle fibres formed within the intact nucleus. The nucleolus is usually also retained and divided between the daughter cells, although it may be expelled from the nucleus, or it may be dispersed within the nucleus but detectable.
The real reasons why we have sex
The evolution of sexual reproduction describes how sexually reproducing animals , plants , fungi and protists could have evolved from a common ancestor that was a single celled eukaryotic species. The evolution of sex contains two related, yet distinct, themes: its origin and its maintenance. The origin of sexual reproduction in prokaryotes is around 2 billion years ago Gya when bacteria started exchanging genes via the processes of conjugation, transformation, and transduction.
This review discusses the evolutionary and scientific implications of considering these three events as part of a single process. Viewed in this way, the SRC is revealed to be a mechanism for efficiently increasing genetic variation, facilitating adaptation to environmental challenges. It also becomes clear that, in terms of cell proliferation, it is appropriate to contrast mitosis with the entire SRC, rather than with meiosis alone.