Write about the evolution of sex in algae.
Answers
Evolution of sex:
The members of Myxophyceae do not show any trace of sexuality. In other classes of algae, the sexuality has been established. Now to trace out the evolution of sex in algae, it becomes necessary to know about the nature of the gametes in beginning. It is thought, that in the beginning the gametes were of similar shape and size.
These gametes were morphologically identical, but physiologically different, e.g., in Ulothrix and certain species of Chlamydomonas, the gametes are of plus and minus strains. This is known as isogamy. Thereafter anisogamy developed. In this process, the two uniting gametes are of different sizes, e.g., in Chlamydomonas braunii and Pandorina. In this condition, the number of divisions in one cell is more or less than the other cell, and therefore, the uniting gametes are unequal in size. Thereafter developed oogamy.
The oogamy is the highly evolved condition of heterogamy. In oogamy, one cell does not divide at all it simply increases in size, accumulates sufficient food material and acts as female cell or egg. The other cell divides repeatedly producing small motile cells, acting as male gametes. However, in Polysiphonia the resultant male gametes are non-motile. Less evolved oogamy is found in Chlamydomonas coccifera, Volvox and Oedogonium.
The evolution of sex in algae has not taken place in any one phylogenetic line. This has taken place along several independent lines. The example of this statement is found in Volvocales, where Gonium is isogamous, Pandorina slightly anisogalnous, Eudorina and Pleodorina marked by anisogamy and Volvox oogamous. This Gonium-Pandorina-Eudorina-Pleodorina-Volvox series also shows progressive somatic differentiation. It has been assumed that it is correlated with the evolution from isogamy to oogamy through anisogamy. Whereas on the other hand, in another genus of Volvocales, i.e., Chlamydomonas, where species within the genus show all gradations from isogamy to oogamy, e.g., Chlamydomonas snowiae is isogamous, C. braunii is anisogamous and C. coccifera is oogamous.
The evolution of sex in algae in algae is:
Sexual reproduction is the universal trait for all living organisms, especially for eukaryotic organisms.
• Algae is derived from the cyanobacteria it reproduces through both sexually and asexually.
• Evolution of sex in algae found in billion years ago. For example, in brown algae, Ectocarpus has haploid chromosomes.
• Sex determination was first found in Green algae. Green algae is the best example of the evolution of sexual reproduction.
• The Sex has been developed in response to conditions and gamets have been developed from zoospores.