Evolutionary Pathway of Sex

Evolutionary Pathway of Sex

Prokaryotes (HGT)

Eukaryotes

Isogamy

Anisogamy
Asexual reproduction: due to costs of sex

Reproduction

Sexual (Amphimixis)

Amphimixis: Fusion of gametes from two organism.

Isogamy

Fusing gametes are of equal size.

Anisogamy (def. male/female)

Fusing gametes are of unequal size.

Asexual

Apomixis

Offspring produced by single mitosis: genetically identical to mother.

Automixis

Normal meiosis, offspring produced by fusion of two pronuclei: may be genetically different from mother.

Parthenogenesis

Unfertilized eggs develop into a new individual (can be male or female).

Facultative parthenogenesis: Female can produce offspring either sexually or asexually. Obligate parthenogenesis: organisms exclusively reproduce through asexual means.

Thelytoky

Unfertilized eggs develop into female.

Apomictic Parthenogenesis

Unfertilized eggs develop into offspring genetically identical to mother.